bigint upgraded to version 3.0 (#5986)

* bigint upgraded to version 3.0

* fixed missing FromHex import in ethcore tests

* fixed missing FromHex import in rpc tests

util/network/src/lib.rs

@@ -66,6 +66,7 @@ extern crate crypto as rcrypto;
 extern crate rand;
 extern crate time;
 extern crate ansi_term; //TODO: remove this
+extern crate rustc_hex;
 extern crate rustc_serialize;
 extern crate igd;
 extern crate libc;