Update setImmediate use in karma specs

spec/javascripts/helpers/vuex_action_helper.js

@@ -89,7 +89,8 @@ export default (
     payload,
   );
 
-  return Promise.resolve(result)
+  return new Promise(setImmediate)
+    .then(() => result)
     .catch(error => {
       validateResults();
       throw error;

spec/javascripts/test_bundle.js

@@ -3,6 +3,7 @@
 */
 
 import $ from 'jquery';
+import 'core-js/features/set-immediate';
 import 'vendor/jasmine-jquery';
 import '~/commons';
 import Vue from 'vue';