如何在react导航v3中使用构造函数方法？

npm install --save react-router-dom@3.x.x

import { Router, Route, browserHistory } from 'react-router';

class App extends React.Component {
  constructor(props) {
    super(props);
  }

  render() {
    return (
      <Router history={browserHistory}>
        <Route path="/" component={Home} />
        <Route path="/about" component={About} />
        <Route path="/contact" component={Contact} />
      </Router>
    );
  }
}

ReactDOM.render(<App />, document.getElementById('root'));