Bump mio (#5763)

* Bump mio

* Fixed warnings

* Update mio to crates.

util/io/Cargo.toml

@@ -7,7 +7,7 @@ version = "1.7.0"
 authors = ["Parity Technologies <admin@parity.io>"]
 
 [dependencies]
-mio = { git = "https://github.com/paritytech/mio" }
+mio = "0.6.8"
 crossbeam = "0.2"
 parking_lot = "0.4"
 log = "0.3"

util/io/src/lib.rs

@@ -54,6 +54,9 @@
 //! }
 //! ```
 
+//TODO: use Poll from mio
+#![allow(deprecated)]
+
 extern crate mio;
 #[macro_use]
 extern crate log as rlog;