const Koa = require('koa'),
    app = new Koa(),
    Router = require('koa-router'),
    router = new Router();

app.use(router.routes());

app.use(ctx => {
    ctx.body = 'Hello World';
});

app.listen(8000);

没有报错，但是报出一条警告：

koa deprecated Support for generators will be removed in v3. See the documentation for examples of how to convert old middleware https://github.com/koajs/koa/blob/master/docs/migration.md server.js:6:5

OK， 那么就是app.use(router.routes());这里写的不好，那么应该怎么写才对呢？事实上我甚至不太清楚这句话是做什么的~

求教，谢谢~