Tinny fixes

It is appeared that socket.io over node.js was unable to work with
RTCMultiConnection-v1.3 because we were declaring and initializing
variables without using keyword "var".

We were setting like this:

sender = Math.round(Math.random() * 60535) + 5000;
socket = io.connect(URL + channel);

However, it must be like this:

var sender = Math.round(Math.random() * 60535) + 5000;
var socket = io.connect(URL + channel);

Link:
https://github.com/muaz-khan/WebRTC-Experiment#use-your-own-socketio-implementation