Catch up to the latest hex package format

Author: parroty

mix.exs

@@ -46,7 +46,7 @@ defmodule OAuth2Ex.Mixfile do
   end
 
   defp package do
-    [ contributors: ["parroty"],
+    [ maintainers: ["parroty"],
       licenses: ["MIT"],
       links: %{"GitHub" => "https://github.com/parroty/oauth2ex"} ]
   end