chore: fix plunkers for IE11

public/resources/js/util.js

@@ -6,7 +6,7 @@ var NgIoUtil = (function () {
 
     NgIoUtil.isDoc = function ($location, lang) {
         var loc = $location.absUrl();
-        return loc.includes('/docs/' + lang + '/');
+        return loc.indexOf('/docs/' + lang + '/') >= 0;
     };
 
     // The following util functions are adapted from _utils-fn.jade.
@@ -19,7 +19,7 @@ var NgIoUtil = (function () {
          *
          * - app/main.ts -> web/main.dart
          * - displaying-data/ts/app/app.component.2.ts -> displaying-data/dart/lib/app_component.dart
-         * 
+         *
          * Notice that the '.2' is dropped from the name.
          */
         if (!_path) return _path;