chore(cargo): update cron requirement from 0.11 to 0.12 (#97)

Updates the requirements on [cron](https://github.com/zslayton/cron) to permit the latest version.
- [Release notes](https://github.com/zslayton/cron/releases)
- [Commits](https://github.com/zslayton/cron/compare/v0.11.0...v0.12.0)

---
updated-dependencies:
- dependency-name: cron
  dependency-type: direct:production
...

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Cargo.toml

@@ -20,7 +20,7 @@ blocking = ["diesel", "diesel-derive-enum", "dotenv"]
 asynk = ["bb8-postgres",  "postgres-types", "tokio", "async-trait", "async-recursion"]
 
 [dependencies]
-cron = "0.11"
+cron = "0.12"
 chrono = "0.4"
 hex = "0.4"
 log = "0.4"