Initialize a GatewayList object from a json dictionary.

def _from_dict(cls, _dict):
        """Initialize a GatewayList object from a json dictionary."""
        args = {}
        if 'gateways' in _dict:
            args['gateways'] = [
                Gateway._from_dict(x) for x in (_dict.get('gateways'))
            ]
        return cls(**args)