Koa with http2 cannot get request
I use http2 with koa.

```
http2.createServer(app.callback()).listen(3000, () => {
  console.info('===========================================');
  console.info('===== Server is running at port: 3000 =====');
  console.info('===========================================');
});
```

But when I  use browser to hit `127.0.0.1:3000`. Server didn't get any request at console.
I am not sure it is koa or middleware's issue.
Here is my sample https://github.com/Rukeith/blog-server/tree/http2-demo