Saw a reply on the original pull request that the WebSocket using a random port broke their set up so I added a `--websocket` or `-w` argument similar to the `-p` argument to allow manually setting this port also.
Fixes#4495
Here's my approach for replacing the XHR on-demand-entries pinger #1364#4495. I'm not sure if this is the way everyone wants to accomplish this since I saw mention of using a separate server and port for the dynamic entries websocket, but thought this would be a fairly clean solution since it doesn't need that.
With this method the only change when using a custom server is you have to listen for the upgrade event and pass it to next.getRequestHandler(). Example:
```
const server = app.listen(port)
const handleRequest = next.getRequestHandler()
if(dev) {
server.on('upgrade', handleRequest)
}
```
