Air-pressure sensor not supported

Thank you very much for homebridge-mi-aqara, it's great. I used homebridge-aqara, but your implementation is superior!.

Sorry, my English is bad!

I tell you, the TemperatureAndHumiditySensor2 device, in addition to supporting temperature and humidity, also has an atmospheric pressure sensor (air pressure). This data is not being supported in homebridge-mi-aqara. Could you include it?

If you need me to do testing, just ask me, I'll gladly do it.

Regards,
Angel
<img width="375" alt="image" src="https://user-images.githubusercontent.com/296882/35841184-84c8ceca-0ad9-11e8-98f2-ca57cadfdc38.png">
