Compatibility with the bitget API v2

[YVINEE]

Hi,
To be compatible with the bitget API v2, there is a little change to do.
Indeed, we have already the possibility to set the websocket url to 'wss://ws.bitget.com/v2/ws/private' in this way:

        websocket_client = BitgetWsClient(ws_url='wss://ws.bitget.com/v2/ws/private',
                                api_key=json_config['apiKey'],
                                api_secret=json_config['secret'],
                                passphrase=json_config['password'],
                                verbose=True) \
            .error_listener(handel_error) \
            .build()
        channels = [SubscribeReq('SPOT', 'orders', coin + 'USDT')]

The only problem is when we subscribe SPOT is transformed in spot (lowercase) which generate the error 30016 Param error.
Could you change the line :
chanel.inst_type = str(chanel.inst_type).lower()
by
chanel.inst_type = str(chanel.inst_type)
in the file stream.py in order to solve this problem.
Thanks,
Yann