Discard sensor temperature alert status flags (#46)
Per [specification the broadcast message](https://github.com/OpenWonderLabs/SwitchBotAPI-BLE/blob/latest/devicetypes/meter.md#meter-broadcast-message-format) byte 3 includes the device temperature and humidity alert status flags and the decimal temperature (in the last 4 bits). Therefore, only the last 4 bits should be considered to extract the temperature in Celsius.
Without this fix, when the sensor is within the alert range the flags cause the temperature to interpreted incorrectly.