rename _getId -> _retrieveId to prevent confusion with id getter

lib/peer.js

@@ -65,13 +65,13 @@ function Peer(id, options) {
     this._init();
   } else {
     this.id = null;
-    this._getId();
+    this._retrieveId();
   }
 };
 
 util.inherits(Peer, EventEmitter);
 
-Peer.prototype._getId = function(cb) {  
+Peer.prototype._retrieveId = function(cb) {  
   var self = this;
   try {
     var http = new XMLHttpRequest();