use .append instead of .nodes.add

tests/html/instance_of_test.dart

 library InstanceOfTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 main() {
   CanvasElement canvas;
 
   canvas = new Element.tag('canvas');
   canvas.attributes['width'] = '100';
   canvas.attributes['height'] = '100';
-  document.body.nodes.add(canvas);
+  document.body.append(canvas);
 
   var isCanvasRenderingContext = predicate((x) => x is CanvasRenderingContext,
       'is a CanvasRenderingContext');
   var isCanvasRenderingContext2D =
       predicate((x) => x is CanvasRenderingContext2D,
       'is a CanvasRenderingContext2D');
   var isElement = predicate((x) => x is Element, 'is an Element');
   var isCanvasElement =
       predicate((x) => x is CanvasElement, 'is a CanvasElement');
   var isImageData = predicate((x) => x is ImageData, 'is an ImageData');
@@ skipping 38 matching lines @@
     expect(bytes, isNot(isCanvasElement));
     expect(bytes, isNot(isImageData));
     expect(bytes, isIntList);
 
     // FIXME: Ensure this is an SpanElement when we next update
     // WebKit IDL.
     var span = new Element.tag('span');
     expect(span, isElement);
   });
 }