too many arguments on_disconnect / 'flag' argument is too much

[divingyo]

Hi,
two exception raised when the connection to the mqtt broker is lost.
main.py -> TypeError: on_disconnect() missing 1 required positional argument: 'rc'
and
client.py -> TypeError: mqtt_on_disconnect() missing 1 required positional argument: 'rc'

there are 4 arguments for 'on_disconnect(client, userdata, flags, rc)' and 'mqtt_on_disconnect(self, client, userdata, flags, rc)'
but according to the paho documentation there should only be 3 -> on_disconnect(client, userdata, rc)