no need for mut self for now method

src/keepalive.rs

@@ -77,7 +77,7 @@ impl<R, E, F> KeepAliveService<R, E, F>
 where
     F: Fn() -> E,
 {
-    pub fn new(ka: Duration, mut timer: LowResTimerService, f: F) -> Self {
+    pub fn new(ka: Duration, timer: LowResTimerService, f: F) -> Self {
         let expire = timer.now() + ka;
         KeepAliveService {
             f,

src/timer.rs

@@ -66,7 +66,7 @@ impl LowResTimerService {
 
     /// Get current time. This function has to be called from
     /// future's poll method, otherwise it panics.
-    pub fn now(&mut self) -> Instant {
+    pub fn now(&self) -> Instant {
         let cur = self.0.borrow().current.clone();
         if let Some(cur) = cur {
             cur