Add battery state to Temperature Sensor

These work the same as the body sensors, so we can simply import
the existing capability.

lib/devices/gateway/sensor_ht.js

@@ -3,8 +3,9 @@
 
 const SubDevice = require('./subdevice');
 const { Temperature, Humidity } = require('../capabilities/sensor');
+const Voltage = require('./voltage');
 
-module.exports = class SensorHT extends SubDevice.with(Temperature, Humidity) {
+module.exports = class SensorHT extends SubDevice.with(Temperature, Humidity, Voltage) {
 	constructor(parent, info) {
 		super(parent, info);