Can't invoke next middlewares.

[JiangJie]

I noticed that the following code didn't invoke my next middlewares which was registered behind the vhost.

// without invoke the next server's middlewares or next middleware
return yield vhost.middleware.call(this/*, next*/);

I think the comments /*, next*/ should be cancelled and it works well.(I'm sure)

[wyntau]

如果把注释打开的话，就会运行下一个server中的代码，这应该不是我们想要的