react-router的history问题

Question

import React from 'react';import {render} from 'react-dom';import { Router, Route, hashHistory } from 'react-router';class App extends React.Component {    render() {        return (<h1>App</h1>);    }}render((  <Router history={hashHistory}>    <Route path="/" component={App}/>  </Router>), document.getElementById('root'));报错信息为为什么已经引用了hashHistory却还会报错