Production build does not include factory guy

Fixes adopted-ember-addons#140

index.js

@@ -5,11 +5,17 @@ module.exports = {
 
   included: function(app) {
     this._super.included(app);
+    this.app = app;
     // need to load mockjax in development and test environment since ember tests
     // can be run from browser in development mode
     if (app.tests) {
       app.import(app.bowerDirectory + '/jquery-mockjax/dist/jquery.mockjax.js');
     }
-  }
+  },
 
+  treeFor: function(name) {
+    if(this.app.tests) {
+      return this._super.treeFor.apply(this, arguments);
+    }
+  }
 };