Memory leaks fix

Memory leaks fix, removing previous listeners for the existing clients 

Trace
    at Socket.EventEmitter.addListener (events.js:160:15)
    at Socket.<anonymous> (/home/admin/presence/node_modules/udp-proxy/index.js:84:17)
    at Socket.EventEmitter.emit (events.js:98:17)
    at UDP.onMessage (dgram.js:440:8)
(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Merge pull request #4 from leonardlabuneti/patch-1

Memory leaks fix. Merging pr, thanks :)