MC-4189: IE11 - PageBuilder Does Not Load

- Fix IE 11 loading of TinyMCE

Author: davemacaulay

lib/web/mage/adminhtml/wysiwyg/tiny_mce/setup.js

@@ -30,7 +30,7 @@ define([
 
             _.bindAll(this, 'openFileBrowser');
 
-            config = Object.assign({}, baseConfig, config || {});
+            config = _.extend({}, baseConfig, config || {});
             this.wysiwygInstance = new WysiwygInstancePrototype(htmlId, config);
             this.wysiwygInstance.eventBus = this.eventBus = new window.varienEvents();
         },