Thermostat - Current Temperature not being refreshed
Same issue as #35. The current temperature is not being updated as part of the polling process. I am presently watching the temperature as reported in Smartthings decline, and the temperature in the HomeKit App remain constant.

`homebridge.err` contains the following entries (`homebridge.log` only has initialisation messages):
`Sun, 06 Mar 2016 10:13:05 GMT Accessory [bridge] Getting value for Characteristic "Current Temperature"`
`Sun, 06 Mar 2016 10:13:05 GMT Accessory [bridge] Got Characteristic "Current Temperature" value: 24.7`
`Sun, 06 Mar 2016 10:25:25 GMT Accessory [bridge] Getting value for Characteristic "Current Temperature"`
`Sun, 06 Mar 2016 10:25:25 GMT Accessory [bridge] Got Characteristic "Current Temperature" value: 24.7`
`Sun, 06 Mar 2016 10:25:38 GMT Accessory [bridge] Getting value for Characteristic "Current Temperature"`
`Sun, 06 Mar 2016 10:25:38 GMT Accessory [bridge] Got Characteristic "Current Temperature" value: 24.7`
`Sun, 06 Mar 2016 10:25:44 GMT Accessory [bridge] Getting value for Characteristic "Current Temperature"`
`Sun, 06 Mar 2016 10:25:44 GMT Accessory [bridge] Got Characteristic "Current Temperature" value: 24.7`

During this same window of time, according to the Smartthings Event Log, the temperature declined from 24.4 to 24.3, and it hadn't been 24.7 for at least 90 minutes.

Environment:
- Homebridge-Smartthings: 0.4.3
- Homebridge-Smartthings SmartApp: 0.4.1
- HomeKit App: Eve
- `polling_seconds`: 60
