fix: URL undefined error. (#442)

References tim-hellhake/sonos-adapter#9

Author: mrstegeman

lib/sonos.js

@@ -14,6 +14,7 @@ const RENDERING_ENDPOINT = '/MediaRenderer/RenderingControl/Control'
 const DEVICE_ENDPOINT = '/DeviceProperties/Control'
 
 // Dependencies
+const URL = require('url').URL
 const util = require('util')
 const EventEmitter = require('events').EventEmitter
 const request = require('axios')