Fix build on MacOS

This patch bumps the version of app_dirs to ^1.2.1
See andybarron/app-dirs-rs#29

Author: joojis

Cargo.lock

@@ -5,7 +5,7 @@ license = "AGPL-3.0"
 authors = ["CodeChain Team <[email protected]>"]
 
 [dependencies]
-app_dirs = "^1.1.1"
+app_dirs = "^1.2.1"
 clap = { version = "2", features = ["yaml"] }
 codechain-core = { path = "core" }
 codechain-discovery = { path = "discovery" }