code style fix

components/tree/index.jsx

 import React from 'react';
 import Tree from 'rc-tree';
-var TreeNode = Tree.TreeNode;
-
-var antDTree = React.createClass({
 
+var AntTree = React.createClass({
   render() {
     return <Tree {...this.props} >
       {this.props.children}
     </Tree>;
   }
 });
-antDTree.TreeNode = TreeNode;
-module.exports = antDTree;
+
+AntTree.TreeNode = Tree.TreeNode;
+export default AntTree;