Parser for float fails for GetCompositeSchedule action

[laysauchoa]

The following parser condition does not work properly:

https://github.com/mobilityhouse/ocpp/blob/master/ocpp/messages.py#L220-L222

One can reproduce with the following test:

def test_validate_get_composite_profile_payload():
    message = CallResult(
        unique_id="1234",
        action="GetCompositeSchedule",
        payload={
            'status': 'Accepted',
            'connectorId': 1,
            'scheduleStart': '2021-06-15T14:01:32Z',
            'chargingSchedule': {
                'duration': 60,
                'chargingRateUnit': 'A',
                'chargingSchedulePeriod': [
                    {
                        'startPeriod': 0,
                        'limit': 15.2
                    }
                ]
            }
        })

    validate_payload(message, ocpp_version="1.6")

[laysauchoa]

This closes this issue #218