Fixing case of IE polyfill using deprecated syntax

tools/dom/templates/html/dart2js/impl_HTMLTableElement.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
 
   Element createTBody() {
     if (JS('bool', '!!#.createTBody', this)) {
       return this._createTBody();
     }
     var tbody = new Element.tag('tbody');
-    this.elements.add(tbody);
+    this.children.add(tbody);
     return tbody;
   }
 
   @JSName('createTBody')
   Element _createTBody() native;
 }