Fixing master

Summary:
This PR fixes the flow broken build in master
Closes facebookarchive/draft-js#1631

Differential Revision: D6820135

fbshipit-source-id: 7c393f66f16d6d80065974c3cf7108e2ee9c4a7f

Author: aforismesen

src/stubs/gkx.js

@@ -13,6 +13,6 @@
 
 'use strict';
 
-module.exports = function(name) {
+module.exports = function(name: string) {
   return false;
 };