Relax myxql dependency (#613)

Author: timothyvanderaerden

mix.exs

@@ -92,7 +92,7 @@ defmodule EctoSQL.MixProject do
     if path = System.get_env("MYXQL_PATH") do
       {:myxql, path: path}
     else
-      {:myxql, "~> 0.6.0", optional: true}
+      {:myxql, "~> 0.6", optional: true}
     end
   end