changes RTCPeerConnection iceServers url property to urls

see https://developer.mozilla.org/en-US/docs/Web/API/RTCIceServer/url

lib/util.js

@@ -1,4 +1,4 @@
-var defaultConfig = { iceServers: [{ url: "stun:stun.l.google.com:19302" }] };
+var defaultConfig = {'iceServers': [{ 'urls': 'stun:stun.l.google.com:19302' }]};
 var dataCount = 1;
 
 var BinaryPack = require("js-binarypack");