Fix callbacks to match the expected number of args

[squgeim]

The callbacks _on_open, _on_message and _on_error provided to WebSocketApp had insufficient number of arguments as expected by websocket-client version 0.51.0 (as mentioned in the requirements.txt).

Fixes #38.

[deepbrook]

Seriously? What are these nuggets doing. Version 0.49.0 removed the ws, now they're adding it back? sigh.
Thanks for picking up on this.

[deepbrook]

Just to be on the safe side, please replace the ws parameter with *args.

[agronholm]

With the latest Pysher (1.0.3) and the latest websocket-client (0.53.0) I get these errors:

ERROR:websocket:error from callback <bound method Connection._on_open of <Connection(PysherEventLoop, started daemon 140281593100032)>>: _on_open() missing 1 required positional argument: 'ws'
ERROR:websocket:error from callback <bound method Connection._on_message of <Connection(PysherEventLoop, started daemon 140281593100032)>>: _on_message() missing 1 required positional argument: 'message'

Pysher 1.0.1 does not have this problem. I even tried installing websocket-client 0.51.0 to see if it works together with Pysher 1.0.2 but it doesn't. I get the same errors. Comments?

[agronholm]

The crux of the problem is that websocket-client treats methods as callbacks differently and does not pass the ws argument. It's a stupid design but it is what it is, so please revert this patch!