fix bugs in docs

src/site/articles/improving-the-dom/index.html

 ---
 layout: default
 title: "Improving the DOM"
 rel:
   author: bob-nystrom
 description: "Learn how Dart's HTML library improves the browser programming experience."
 has-permalinks: true
 ---
 
 <h1>Improving the DOM</h1>
@@ skipping 73 matching lines @@
 // Old:
 elem.hasAttribute('name');
 elem.getAttribute('name')
 elem.setAttribute('name', 'value');
 elem.removeAttribute('name');
 </pre>
 </td>
 <td width="50%">
 <pre>
 // New:
-elem.attributes.contains('name');
+elem.attributes.containsKey('name');
 elem.attributes['name'];
 elem.attributes['name'] = 'value';
 elem.attributes.remove('name');
 </pre>
 </td>
 </tr>
 </table>
 
 <p>Likewise, by making <code>nodes</code> and <code>elements</code> full-featured collections, we can get rid of a bunch of methods on <code>Element</code> and <code>Node</code>:</p>
 
@@ skipping 111 matching lines @@
 
 <p>
 Read the <a href="http://api.dartlang.org/html.html">dart:html API docs</a>.
 Also see the following samples, which are included in the
 <a href="/docs/editor/">Dart Editor</a> download and
 which use the dart:html library:
 <a href="http://code.google.com/p/dart/source/browse/trunk/dart/samples/slider/">Slider</a> and
 <a href="http://code.google.com/p/dart/source/browse/trunk/dart/samples/sunflower/">Sunflower</a>.
 </p>