Multiple event firings due to leaking BLE event listeners on Raspberry Pi 3
I'm having trouble getting this running on the Pi. 

I had modified your code to always convert data to utf8. This works perfectly for my devices and running this plugin on my mac. However, when used on the Pi, I get the following error and I can't seem to figure out why as the utf8 module was installed.

```
/usr/local/lib/node_modules/homebridge-lifebot/source/characteristic.js:156
  buffer = Buffer.from(value, 'utf8');
                  ^
TypeError: utf8 is not a function
    at Function.from (native)
    at Function.from (native)
    at BluetoothCharacteristic.toBuffer (/usr/local/lib/node_modules/homebridge-lifebot/source/characteristic.js:156:19)
    at BluetoothCharacteristic.set (/usr/local/lib/node_modules/homebridge-lifebot/source/characteristic.js:118:23)
    at emitMany (events.js:108:13)
    at emit (events.js:182:7)
    at Characteristic.setValue (/usr/local/lib/node_modules/homebridge/node_modules/hap-nodejs/lib/Characteristic.js:155:10)
    at Bridge.<anonymous> (/usr/local/lib/node_modules/homebridge/node_modules/hap-nodejs/lib/Accessory.js:740:22)
    at Array.forEach (native)
    at Bridge.Accessory._handleSetCharacteristics (/usr/local/lib/node_modules/homebridge/node_modules/hap-nodejs/lib/Accessory.js:685:8)
```
