Update based on fixes made in the websockets/ws package

[henriquemps]

Adjust based on fix made in websockets/ws. In this commit: https://github.com/websockets/ws/commit/0aecf0c95b41eaeeec9e265d5f1cb6c96e2f4d08#diff-44c2c0628f273ea1ab6dbb7c1fa81a1765d8adf9fbdd083e2a3b93d8d1cb5f61

[oberstet]

thanks for contributing! unfortunately, this hard codes the protocol to msgpack when the user specifies subprotocols. also, what is the issue being addressed with this change .. this https://github.com/crossbario/autobahn-js/issues/550 ?

[henriquemps]

Exactly, this error. I thought it was interesting to keep the parameter optional and so I put a default value.

When the "protocol" is not specified, the error is displayed, precisely because the validation was changed.

Of course, I believe that at other points where a "join" is used will need to change, as the ws package is accepting "array" and not "string".

[om26er]

We currently limit the ws version to be < 8.0. We'll have to come up with a proper fix for it https://github.com/crossbario/autobahn-js/issues/569