react activeClassname問題？

剛開始學(xué)react，遇到一個(gè)問題，求指點(diǎn)
設(shè)置當(dāng)前顯示路由的class報(bào)錯(cuò)

import React,{ Component } from "react";
import router1 from './router1';
import router2 from './router2';
import router3 from './router3';
import "./main.css";
import {
    BrowserRouter as Router,
    Route,
    Link
}from 'react-router-dom';

class main extends Component {
render() {
    return (
        <Router>
            <div>
                <ul>
                    <li><Link to="/" className="active" activeClassname="current">路由1</Link></li>
                    <li><Link to="/router2" className="active" activeClassname="current">路由2</Link></li>
                    <li><Link to="/router3" className="active" activeClassname="current">路由3</Link></li>
                </ul>
                <hr />
                <Route exact path="/" component={router1} />
                <Route path="/router2" component={router2} />
                <Route path="/router3" component={router3} />
            </div>
        </Router>
    );
}
}

export default main;

提示說換成小寫的，但是換成小寫的不報(bào)錯(cuò)了，卻不起作用？剛學(xué)了一天react，求大佬指點(diǎn)