use .append instead of .nodes.add

tests/html/htmlelement_test.dart

 library ElementTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlConfiguration();
   test('InnerHTML', () {
     Element element = new Element.tag('div');
     element.id = 'test';
     element.innerHtml = 'Hello World';
-    document.body.nodes.add(element);
+    document.body.append(element);
 
     element = document.query('#test');
     expect(element.innerHtml, 'Hello World');
     element.remove();
   });
   test('HTMLTable', () {
     Element table = new Element.tag('table');
 
     TableRowElement row = new Element.tag('tr');
-    table.nodes.add(row);
+    table.append(row);
 
-    row.nodes.add(new Element.tag('td'));
-    row.nodes.add(new Element.tag('td'));
+    row.append(new Element.tag('td'));
+    row.append(new Element.tag('td'));
 
     expect(row.cells.length, 2);
 
     TableRowElement headerRow = table.rows[0];
     expect(headerRow.cells.length, 2);
   });
   test('dataset', () {
     Element div = new Element.tag('div');
 
     expect(div.dataset.isEmpty, isTrue);
@@ skipping 46 matching lines @@
 
     expect(div.dataset.remove('foo'), 'foo-value');
     expect(div.dataset.length, 1);
     expect(div.dataset.isEmpty, isFalse);
 
     div.dataset.clear();
     expect(div.dataset.length, 0);
     expect(div.dataset.isEmpty, isTrue);
   });
 }