Fix compatiblity with websockets>=9.0

[mweinelt]

The client, server, protocol, and auth modules were moved from the websockets package to websockets.legacy sub-package, as part of an upcoming refactoring. Despite the name, they’re still fully supported. The refactoring should be a transparent upgrade for most uses when it’s available. The legacy implementation will be preserved according to the backwards-compatibility policy.

https://websockets.readthedocs.io/en/stable/changelog.html#id5

Fixes: #239

[deztructor]

(Tested: it is working)

[FlorianLudwig]

FYI

hbmqtt is EOL.

https://github.com/beerfactory/hbmqtt/issues/235