Update Route.js

Author: guotie

modules/Route.js

@@ -2,6 +2,7 @@ import React from 'react';
 import invariant from 'invariant';
 import { createRouteFromReactElement } from './RouteUtils';
 import { component, components } from './PropTypes';
+import warning from 'warning';
 
 var { string, bool, func } = React.PropTypes;