How to omit the `X-Powered-By` HTTP response header to avoid exposing Ratchet version to potential attackers?
Hi,

The `X-Powered-By` header sent by Ratchet describes the technologie used by the server. Therefore this info exposes the server to malicious attackers who can find vulnerabilities easier.

Below  are the two files that add this header:

https://github.com/ratchetphp/Ratchet/blob/5012dc954541b40c5599d286fd40653f5716a38f/src/Ratchet/WebSocket/WsServer.php#L117-L119

https://github.com/ratchetphp/Ratchet/blob/5012dc954541b40c5599d286fd40653f5716a38f/src/Ratchet/Http/CloseResponseTrait.php#L15-L17

I have tried everything to hide this header with the decorators, but I can't achieve it. I spent my day there. The handshake negotiator is implicitly called inside the `Ratchet\WebSocket\WsServer` class and I can't modify the response that is directly sent. I didn't try to modify the header sent by the  `Ratchet\Http/CloseResponseTrait` class, since I was unable to hide the one from the  `Ratchet\WebSocket\WsServer` class... 

Has anyone ever succedeed in changing/removing this header with the decorators? If so, how? Am I missing something obvious? Or is there indeed a issue in hiding this header? I ask for your help to clarify the situation, thanks!

Related issues and PRs:
- https://github.com/ratchetphp/Ratchet/issues/932
- https://github.com/ratchetphp/Ratchet/issues/650
- https://github.com/ratchetphp/Ratchet/pull/524

Regards.