Update env_logger requirement from 0.5 to 0.6 (paritytech#335)

Updates the requirements on [env_logger](https://github.com/sebasmagri/env_logger) to permit the latest version.
- [Release notes](https://github.com/sebasmagri/env_logger/releases)
- [Commits](https://github.com/sebasmagri/env_logger/commits/v0.6.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

ipc/Cargo.toml

@@ -17,7 +17,7 @@ parity-tokio-ipc = "0.1"
 parking_lot = "0.6"
 
 [dev-dependencies]
-env_logger = "0.5"
+env_logger = "0.6"
 lazy_static = "1.0"
 
 [target.'cfg(not(windows))'.dev-dependencies]

minihttp/Cargo.toml

@@ -20,7 +20,7 @@ tokio-proto = { git = "https://github.com/tomusdrw/tokio-proto" }
 tokio-service = "0.1"
 
 [dev-dependencies]
-env_logger = "0.5"
+env_logger = "0.6"
 reqwest = "0.6"
 
 [badges]

stdio/Cargo.toml

@@ -19,7 +19,7 @@ tokio-stdin-stdout = "0.1.4"
 
 [dev-dependencies]
 lazy_static = "1.0"
-env_logger = "0.5"
+env_logger = "0.6"
 
 [badges]
 travis-ci = { repository = "solana-labs/jsonrpc", branch = "solana-0.3"}

tcp/Cargo.toml

@@ -17,7 +17,7 @@ solana-jsonrpc-server-utils = { version = "0.3.0", path = "../server-utils" }
 
 [dev-dependencies]
 lazy_static = "1.0"
-env_logger = "0.5"
+env_logger = "0.6"
 
 [badges]
 travis-ci = { repository = "solana-labs/jsonrpc", branch = "solana-0.3"}