LibraryMQTT not usable with paho-mqtt 2.0.0

[BriceBoy]

ValueError: Unsupported callback API version: version 2.0 added a callback_api_version, see migrations.md for details

Traceback (most recent call last):
  File "C:\WINDOWS\ServiceProfiles\NetworkService\AppData\Roaming\Python\Python37\site-packages\MQTTLibrary\MQTTKeywords.py", line 71, in connect
    self._mqttc = mqtt.Client(client_id, clean_session)
  File "C:\WINDOWS\ServiceProfiles\NetworkService\AppData\Roaming\Python\Python37\site-packages\paho\mqtt\client.py", line 767, in __init__
    "Unsupported callback API version: version 2.0 added a callback_api_version, see migrations.md for details"
ValueError: Unsupported callback API version: version 2.0 added a callback_api_version, see migrations.md for details

[romanliv]

I tried to address this issue in #35, maybe someone with enough permissions can review and merge it if the fix is ok.

[BriceBoy]

Thank you ! I hope this will be done ^^