How to get Socket.io 2 to work with Koa 2?
How can I use socket.io with koa 2? I tried the following but does not work:

   ```
    import Koa from 'koa'
    import socket from 'socket.io'
    import http from 'http'
    
    const app = new Koa()
    
    // Basic.
    app.use(async ctx => {
      ctx.body = 'Hello World'
    })
    
    const server = http.createServer(app.callback())
    const io = new socket(server)
    
    io.on('connection', function(socket){
        console.log('a user connected')
    })
    
    server.listen(3000)
```

I don't see `'a user connected'` on my terminal.

Any ideas?