diff --git a/vendor/github.com/drone/envsubst/parse/node.go b/vendor/github.com/drone/envsubst/parse/node.go
new file mode 100644
index 000000000..09787eb92
--- /dev/null
+++ b/vendor/github.com/drone/envsubst/parse/node.go
@@ -0,0 +1,86 @@
+package parse
+
+// Node is an element in the parse tree.
+type Node interface {
+	node()
+}
+
+// empty string node
+var empty = new(TextNode)
+
+// a template is represented by a tree consisting of one
+// or more of the following nodes.
+type (
+	// TextNode represents a string of text.
+	TextNode struct {
+		Value string
+	}
+
+	// FuncNode represents a string function.
+	FuncNode struct {
+		Param string
+		Name  string
+		Args  []Node
+	}
+
+	// ListNode represents a list of nodes.
+	ListNode struct {
+		Nodes []Node
+	}
+
+	// ParamNode struct{
+	// 	Name string
+	// }
+	//
+	// CaseNode struct {
+	// 	Name string
+	// 	First bool
+	// }
+	//
+	// LowerNode struct {
+	// 	Name string
+	// 	First bool
+	// }
+	//
+	// SubstrNode struct {
+	// 	Name string
+	// 	Pos Node
+	// 	Len Node
+	// }
+	//
+	// ReplaceNode struct {
+	// 	Name string
+	// 	Substring Node
+	// 	Replacement Node
+	// }
+	//
+	// TrimNode struct{
+	//
+	// }
+	//
+	// DefaultNode struct {
+	// 	Name string
+	// 	Default Node
+	// }
+)
+
+// newTextNode returns a new TextNode.
+func newTextNode(text string) *TextNode {
+	return &TextNode{Value: text}
+}
+
+// newListNode returns a new ListNode.
+func newListNode(nodes ...Node) *ListNode {
+	return &ListNode{Nodes: nodes}
+}
+
+// newFuncNode returns a new FuncNode.
+func newFuncNode(name string) *FuncNode {
+	return &FuncNode{Param: name}
+}
+
+// node() defines the node in a parse tree
+
+func (*TextNode) node() {}
+func (*ListNode) node() {}
+func (*FuncNode) node() {}
diff --git a/vendor/github.com/drone/envsubst/parse/parse.go b/vendor/github.com/drone/envsubst/parse/parse.go
new file mode 100644
index 000000000..f6ab3bbf2
--- /dev/null
+++ b/vendor/github.com/drone/envsubst/parse/parse.go
@@ -0,0 +1,371 @@
+package parse
+
+import "errors"
+
+// ErrBadSubstitution represents a substitution parsing error.
+var ErrBadSubstitution = errors.New("bad substitution")
+
+// Tree is the representation of a single parsed SQL statement.
+type Tree struct {
+	Root Node
+
+	// Parsing only; cleared after parse.
+	scanner *scanner
+}
+
+// Parse parses the string and returns a Tree.
+func Parse(buf string) (*Tree, error) {
+	t := new(Tree)
+	t.scanner = new(scanner)
+	return t.Parse(buf)
+}
+
+// Parse parses the string buffer to construct an ast
+// representation for expansion.
+func (t *Tree) Parse(buf string) (tree *Tree, err error) {
+	t.scanner.init(buf)
+	t.Root, err = t.parseAny()
+	return t, err
+}
+
+func (t *Tree) parseAny() (Node, error) {
+	t.scanner.accept = acceptRune
+	t.scanner.mode = scanIdent | scanLbrack
+
+	switch t.scanner.scan() {
+	case tokenIdent:
+		left := newTextNode(
+			t.scanner.string(),
+		)
+		right, err := t.parseAny()
+		switch {
+		case err != nil:
+			return nil, err
+		case right == empty:
+			return left, nil
+		}
+		return newListNode(left, right), nil
+	case tokenEOF:
+		return empty, nil
+	case tokenLbrack:
+		left, err := t.parseFunc()
+		if err != nil {
+			return nil, err
+		}
+
+		right, err := t.parseAny()
+		switch {
+		case err != nil:
+			return nil, err
+		case right == empty:
+			return left, nil
+		}
+		return newListNode(left, right), nil
+	}
+
+	return nil, ErrBadSubstitution
+}
+
+func (t *Tree) parseFunc() (Node, error) {
+	switch t.scanner.peek() {
+	case '#':
+		return t.parseLenFunc()
+	}
+
+	var name string
+	t.scanner.accept = acceptIdent
+	t.scanner.mode = scanIdent
+
+	switch t.scanner.scan() {
+	case tokenIdent:
+		name = t.scanner.string()
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	switch t.scanner.peek() {
+	case ':':
+		return t.parseDefaultOrSubstr(name)
+	case '=':
+		return t.parseDefaultFunc(name)
+	case ',', '^':
+		return t.parseCasingFunc(name)
+	case '/':
+		return t.parseReplaceFunc(name)
+	case '#':
+		return t.parseRemoveFunc(name, acceptHashFunc)
+	case '%':
+		return t.parseRemoveFunc(name, acceptPercentFunc)
+	}
+
+	t.scanner.accept = acceptIdent
+	t.scanner.mode = scanRbrack
+	switch t.scanner.scan() {
+	case tokenRbrack:
+		return newFuncNode(name), nil
+	default:
+		return nil, ErrBadSubstitution
+	}
+}
+
+// parse a substitution function parameter.
+func (t *Tree) parseParam(accept acceptFunc, mode byte) (Node, error) {
+	t.scanner.accept = accept
+	t.scanner.mode = mode | scanLbrack
+	switch t.scanner.scan() {
+	case tokenLbrack:
+		return t.parseFunc()
+	case tokenIdent:
+		return newTextNode(
+			t.scanner.string(),
+		), nil
+	default:
+		return nil, ErrBadSubstitution
+	}
+}
+
+// parse either a default or substring substitution function.
+func (t *Tree) parseDefaultOrSubstr(name string) (Node, error) {
+	t.scanner.read()
+	r := t.scanner.peek()
+	t.scanner.unread()
+	switch r {
+	case '=', '-', '?', '+':
+		return t.parseDefaultFunc(name)
+	default:
+		return t.parseSubstrFunc(name)
+	}
+}
+
+// parses the ${param:offset} string function
+// parses the ${param:offset:length} string function
+func (t *Tree) parseSubstrFunc(name string) (Node, error) {
+	node := new(FuncNode)
+	node.Param = name
+
+	t.scanner.accept = acceptOneColon
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		node.Name = t.scanner.string()
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	// scan arg[1]
+	{
+		param, err := t.parseParam(rejectColonClose, scanIdent)
+		if err != nil {
+			return nil, err
+		}
+
+		// param.Value = t.scanner.string()
+		node.Args = append(node.Args, param)
+	}
+
+	// expect delimiter or close
+	t.scanner.accept = acceptColon
+	t.scanner.mode = scanIdent | scanRbrack
+	switch t.scanner.scan() {
+	case tokenRbrack:
+		return node, nil
+	case tokenIdent:
+		// no-op
+	default:
+		return nil, ErrBadSubstitution
+	}
+	// err := t.consumeDelimiter(acceptColon, scanIdent|scanRbrack)
+	// if err != nil {
+	// 	return nil, err
+	// }
+
+	// scan arg[2]
+	{
+		param, err := t.parseParam(acceptNotClosing, scanIdent)
+		if err != nil {
+			return nil, err
+		}
+		node.Args = append(node.Args, param)
+	}
+
+	return node, t.consumeRbrack()
+}
+
+// parses the ${param%word} string function
+// parses the ${param%%word} string function
+// parses the ${param#word} string function
+// parses the ${param##word} string function
+func (t *Tree) parseRemoveFunc(name string, accept acceptFunc) (Node, error) {
+	node := new(FuncNode)
+	node.Param = name
+
+	t.scanner.accept = accept
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		node.Name = t.scanner.string()
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	// scan arg[1]
+	{
+		param, err := t.parseParam(acceptNotClosing, scanIdent)
+		if err != nil {
+			return nil, err
+		}
+
+		// param.Value = t.scanner.string()
+		node.Args = append(node.Args, param)
+	}
+
+	return node, t.consumeRbrack()
+}
+
+// parses the ${param/pattern/string} string function
+// parses the ${param//pattern/string} string function
+// parses the ${param/#pattern/string} string function
+// parses the ${param/%pattern/string} string function
+func (t *Tree) parseReplaceFunc(name string) (Node, error) {
+	node := new(FuncNode)
+	node.Param = name
+
+	t.scanner.accept = acceptReplaceFunc
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		node.Name = t.scanner.string()
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	// scan arg[1]
+	{
+		param, err := t.parseParam(acceptNotSlash, scanIdent|scanEscape)
+		if err != nil {
+			return nil, err
+		}
+		node.Args = append(node.Args, param)
+	}
+
+	// expect delimiter
+	t.scanner.accept = acceptSlash
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		// no-op
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	{
+		param, err := t.parseParam(acceptNotClosing, scanIdent)
+		if err != nil {
+			return nil, err
+		}
+		node.Args = append(node.Args, param)
+	}
+
+	return node, t.consumeRbrack()
+}
+
+// parses the ${parameter=word} string function
+// parses the ${parameter:=word} string function
+// parses the ${parameter:-word} string function
+// parses the ${parameter:?word} string function
+// parses the ${parameter:+word} string function
+func (t *Tree) parseDefaultFunc(name string) (Node, error) {
+	node := new(FuncNode)
+	node.Param = name
+
+	t.scanner.accept = acceptDefaultFunc
+	if t.scanner.peek() == '=' {
+		t.scanner.accept = acceptOneEqual
+	}
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		node.Name = t.scanner.string()
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	// scan arg[1]
+	{
+		param, err := t.parseParam(acceptNotClosing, scanIdent)
+		if err != nil {
+			return nil, err
+		}
+
+		// param.Value = t.scanner.string()
+		node.Args = append(node.Args, param)
+	}
+
+	return node, t.consumeRbrack()
+}
+
+// parses the ${param,} string function
+// parses the ${param,,} string function
+// parses the ${param^} string function
+// parses the ${param^^} string function
+func (t *Tree) parseCasingFunc(name string) (Node, error) {
+	node := new(FuncNode)
+	node.Param = name
+
+	t.scanner.accept = acceptCasingFunc
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		node.Name = t.scanner.string()
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	return node, t.consumeRbrack()
+}
+
+// parses the ${#param} string function
+func (t *Tree) parseLenFunc() (Node, error) {
+	node := new(FuncNode)
+
+	t.scanner.accept = acceptOneHash
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		node.Name = t.scanner.string()
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	t.scanner.accept = acceptIdent
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		node.Param = t.scanner.string()
+	default:
+		return nil, ErrBadSubstitution
+	}
+
+	return node, t.consumeRbrack()
+}
+
+// consumeRbrack consumes a right closing bracket. If a closing
+// bracket token is not consumed an ErrBadSubstitution is returned.
+func (t *Tree) consumeRbrack() error {
+	t.scanner.mode = scanRbrack
+	if t.scanner.scan() != tokenRbrack {
+		return ErrBadSubstitution
+	}
+	return nil
+}
+
+// consumeDelimiter consumes a function argument delimiter. If a
+// delimiter is not consumed an ErrBadSubstitution is returned.
+// func (t *Tree) consumeDelimiter(accept acceptFunc, mode uint) error {
+// 	t.scanner.accept = accept
+// 	t.scanner.mode = mode
+// 	if t.scanner.scan() != tokenRbrack {
+// 		return ErrBadSubstitution
+// 	}
+// 	return nil
+// }
diff --git a/vendor/github.com/drone/envsubst/parse/scan.go b/vendor/github.com/drone/envsubst/parse/scan.go
new file mode 100644
index 000000000..c598e9bc8
--- /dev/null
+++ b/vendor/github.com/drone/envsubst/parse/scan.go
@@ -0,0 +1,275 @@
+package parse
+
+import (
+	"unicode"
+	"unicode/utf8"
+)
+
+// eof rune sent when end of file is reached
+var eof = rune(0)
+
+// token is a lexical token.
+type token uint
+
+// list of lexical tokens.
+const (
+	// special tokens
+	tokenIllegal token = iota
+	tokenEOF
+
+	// identifiers and literals
+	tokenIdent
+
+	// operators and delimiters
+	tokenLbrack
+	tokenRbrack
+	tokenQuote
+)
+
+// predefined mode bits to control recognition of tokens.
+const (
+	scanIdent byte = 1 << iota
+	scanLbrack
+	scanRbrack
+	scanEscape
+)
+
+// returns true if rune is accepted.
+type acceptFunc func(r rune, i int) bool
+
+// scanner implements a lexical scanner that reads unicode
+// characters and tokens from a string buffer.
+type scanner struct {
+	buf   string
+	pos   int
+	start int
+	width int
+	mode  byte
+
+	accept acceptFunc
+}
+
+// init initializes a scanner with a new buffer.
+func (s *scanner) init(buf string) {
+	s.buf = buf
+	s.pos = 0
+	s.start = 0
+	s.width = 0
+	s.accept = nil
+}
+
+// read returns the next unicode character. It returns eof at
+// the end of the string buffer.
+func (s *scanner) read() rune {
+	if s.pos >= len(s.buf) {
+		s.width = 0
+		return eof
+	}
+	r, w := utf8.DecodeRuneInString(s.buf[s.pos:])
+	s.width = w
+	s.pos += s.width
+	return r
+}
+
+func (s *scanner) unread() {
+	s.pos -= s.width
+}
+
+// skip skips over the curring unicode character in the buffer
+// by slicing and removing from the buffer.
+func (s *scanner) skip() {
+	l := s.buf[:s.pos-1]
+	r := s.buf[s.pos:]
+	s.buf = l + r
+}
+
+// peek returns the next unicode character in the buffer without
+// advancing the scanner. It returns eof if the scanner's position
+// is at the last character of the source.
+func (s *scanner) peek() rune {
+	r := s.read()
+	s.unread()
+	return r
+}
+
+// string returns the string corresponding to the most recently
+// scanned token. Valid after calling scan().
+func (s *scanner) string() string {
+	return s.buf[s.start:s.pos]
+}
+
+// scan reads the next token or Unicode character from source and
+// returns it. It returns EOF at the end of the source.
+func (s *scanner) scan() token {
+	s.start = s.pos
+	r := s.read()
+	switch {
+	case r == eof:
+		return tokenEOF
+	case s.scanLbrack(r):
+		return tokenLbrack
+	case s.scanRbrack(r):
+		return tokenRbrack
+	case s.scanIdent(r):
+		return tokenIdent
+	}
+	return tokenIllegal
+}
+
+// scanIdent reads the next token or Unicode character from source
+// and returns true if the Ident character is accepted.
+func (s *scanner) scanIdent(r rune) bool {
+	if s.mode&scanIdent == 0 {
+		return false
+	}
+	if s.scanEscaped(r) {
+		s.skip()
+	} else if !s.accept(r, s.pos-s.start) {
+		return false
+	}
+loop:
+	for {
+		r := s.read()
+		switch {
+		case r == eof:
+			s.unread()
+			break loop
+		case s.scanLbrack(r):
+			s.unread()
+			s.unread()
+			break loop
+		}
+		if s.scanEscaped(r) {
+			s.skip()
+			continue
+		}
+		if !s.accept(r, s.pos-s.start) {
+			s.unread()
+			break loop
+		}
+	}
+	return true
+}
+
+// scanLbrack reads the next token or Unicode character from source
+// and returns true if the open bracket is encountered.
+func (s *scanner) scanLbrack(r rune) bool {
+	if s.mode&scanLbrack == 0 {
+		return false
+	}
+	if r == '$' {
+		if s.read() == '{' {
+			return true
+		}
+		s.unread()
+	}
+	return false
+}
+
+// scanRbrack reads the next token or Unicode character from source
+// and returns true if the closing bracket is encountered.
+func (s *scanner) scanRbrack(r rune) bool {
+	if s.mode&scanRbrack == 0 {
+		return false
+	}
+	return r == '}'
+}
+
+// scanEscaped reads the next token or Unicode character from source
+// and returns true if it being escaped and should be sipped.
+func (s *scanner) scanEscaped(r rune) bool {
+	if s.mode&scanEscape == 0 {
+		return false
+	}
+	if r != '\\' {
+		return false
+	}
+	switch s.peek() {
+	case '/', '\\':
+		return true
+	default:
+		return false
+	}
+}
+
+//
+// scanner functions accept or reject runes.
+//
+
+func acceptRune(r rune, i int) bool {
+	return true
+}
+
+func acceptIdent(r rune, i int) bool {
+	return unicode.IsLetter(r) || unicode.IsDigit(r) || r == '_'
+}
+
+func acceptColon(r rune, i int) bool {
+	return r == ':'
+}
+
+func acceptOneHash(r rune, i int) bool {
+	return r == '#' && i == 1
+}
+
+func acceptNone(r rune, i int) bool {
+	return false
+}
+
+func acceptNotClosing(r rune, i int) bool {
+	return r != '}'
+}
+
+func acceptHashFunc(r rune, i int) bool {
+	return r == '#' && i < 3
+}
+
+func acceptPercentFunc(r rune, i int) bool {
+	return r == '%' && i < 3
+}
+
+func acceptDefaultFunc(r rune, i int) bool {
+	switch {
+	case i == 1 && r == ':':
+		return true
+	case i == 2 && (r == '=' || r == '-' || r == '?' || r == '+'):
+		return true
+	default:
+		return false
+	}
+}
+
+func acceptReplaceFunc(r rune, i int) bool {
+	switch {
+	case i == 1 && r == '/':
+		return true
+	case i == 2 && (r == '/' || r == '#' || r == '%'):
+		return true
+	default:
+		return false
+	}
+}
+
+func acceptOneEqual(r rune, i int) bool {
+	return i == 1 && r == '='
+}
+
+func acceptOneColon(r rune, i int) bool {
+	return i == 1 && r == ':'
+}
+
+func rejectColonClose(r rune, i int) bool {
+	return r != ':' && r != '}'
+}
+
+func acceptSlash(r rune, i int) bool {
+	return r == '/'
+}
+
+func acceptNotSlash(r rune, i int) bool {
+	return r != '/'
+}
+
+func acceptCasingFunc(r rune, i int) bool {
+	return (r == ',' || r == '^') && i < 3
+}
diff --git a/vendor/vendor.json b/vendor/vendor.json
index e5459cea2..2102f5ba1 100644
--- a/vendor/vendor.json
+++ b/vendor/vendor.json
@@ -59,6 +59,12 @@
 			"revision": "3e65ae5fd2d944d56fdf52cb3f887247498d50e9",
 			"revisionTime": "2017-01-18T15:01:55Z"
 		},
+		{
+			"checksumSHA1": "LPKfsjm4AYVgCLVcAWnQdSpt5SA=",
+			"path": "github.com/drone/envsubst/parse",
+			"revision": "3e65ae5fd2d944d56fdf52cb3f887247498d50e9",
+			"revisionTime": "2017-01-18T15:01:55Z"
+		},
 		{
 			"path": "github.com/eknkc/amber",
 			"revision": "144da19a9994994c069f0693294a66dd310e14a4",