cargo: add env_filter and libmdns

Cargo.toml

@@ -5,8 +5,10 @@ authors = ["Alexandre Janniaux <ajanni@videolabs.io>"]
 edition = "2018"
 
 [dependencies]
-rocket = "0.4.2"
-rocket_contrib = { version = "0.4.2", features = ["json"] }
+rocket = "0.4"
+rocket_contrib = { version = "0.4", features = ["json"] }
 serde = "1.0"
 serde_json = "1.0"
 serde_derive = "1.0"
+libmdns = "0.2"
+env_logger = "0.6"