fix: correctly detect support for document.registerElement

Author: btford

test/patch/registerElement.spec.js

@@ -6,7 +6,7 @@
 'use strict';
 
 describe('document.registerElement', function () {
-  if (!'registerElement' in document) {
+  if (!('registerElement' in document)) {
     console.log('WARNING: skipping document.registerElement test (missing this API)');
     return;
   }

zone.js

@@ -512,7 +512,7 @@ Zone.patchMutationObserverClass = function (className) {
 };
 
 Zone.patchRegisterElement = function () {
-  if (!'registerElement' in document) {
+  if (!('registerElement' in document)) {
     return;
   }
   var _registerElement = document.registerElement;