Emergency Fix: Change PFX loading behaviour

I have received a multitude of errors while trying to use the protocolOptions object.
The PFX buffer does not seem to work (converted to a string or not) when putting it in protocolOptions.

So I changed the behaviour to load a file path instead. But I assume you guys will be able to figure out what causes these bugs.

PS: The passphrase seems to be required by SocketCluster, but not by the HTTPS module.