Inline cache mock for DependencyGraph-test

Reviewed By: davidaurelio

Differential Revision: D2629211

fb-gh-sync-id: ade0bf4e486b58ecbc9a29eb3bdb61286eebb3d5

packager/react-packager/__mocks__/debug.js

@@ -8,6 +8,4 @@
  */
 'use strict';
 
-module.exports = function() {
-  return function() {};
-};
+module.exports = () => () => {};