Remove some `getDOMNode` from docs and examples

_js/examples/markdown.js

@@ -6,7 +6,7 @@ var MarkdownEditor = React.createClass({
     return {value: 'Type some *markdown* here!'};
   },
   handleChange: function() {
-    this.setState({value: this.refs.textarea.getDOMNode().value});
+    this.setState({value: React.findDOMNode(this.refs.textarea).value});
   },
   render: function() {
     return (

_js/live_editor.js

@@ -21,7 +21,7 @@ var CodeMirrorEditor = React.createClass({
   componentDidMount: function() {
     if (IS_MOBILE) return;
 
-    this.editor = CodeMirror.fromTextArea(this.refs.editor.getDOMNode(), {
+    this.editor = CodeMirror.fromTextArea(React.findDOMNode(this.refs.editor), {
       mode: 'javascript',
       lineNumbers: this.props.lineNumbers,
       lineWrapping: true,
@@ -194,7 +194,7 @@ var ReactPlayground = React.createClass({
   },
 
   executeCode: function() {
-    var mountNode = this.refs.mount.getDOMNode();
+    var mountNode = React.findDOMNode(this.refs.mount);
 
     try {
       React.unmountComponentAtNode(mountNode);