use .append instead of .nodes.add

tests/html/htmlcollection_test.dart

 library ElementListTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 // Test that List<Element> implements List<T>
 main() {
   Element insertTestDiv() {
     Element element = new Element.tag('div');
     element.innerHtml = r"""
@@ skipping 10 matching lines @@
 <input type="checkbox" name="s4" value="4">
 </div>
 <div id='noneChecked'>
 <input type="checkbox" name="n1" value="1">
 <input type="checkbox" name="n2" value="2">
 <input type="checkbox" name="n3" value="3">
 <input type="checkbox" name="n4" value="4">
 </div>
 <div id='emptyDiv'></div>
 """;
-    document.body.nodes.add(element);
+    document.body.append(element);
     return element;
   }
 
   useHtmlConfiguration();
 
   test('IsList', () {
     Element root = insertTestDiv();
 
     List<Element> eachChecked =
         document.query('#allChecked').children;
@@ skipping 226 matching lines @@
     expect(someChecked.lastIndexOf(someChecked[3], 2), -1);
 
     expect(someChecked.lastIndexOf(noneChecked[0], 3), -1);
     expect(noneChecked.lastIndexOf(someChecked[0], 3), -1);
     expect(someChecked.lastIndexOf(noneChecked[1], 3), -1);
     expect(noneChecked.lastIndexOf(someChecked[1], 3), -1);
 
     root.remove();
   });
 }