no need for "self" in CallbackFiller now

lib/callback_filler.js

@@ -3,10 +3,8 @@ function CallbackFiller() {
 }
 
 CallbackFiller.prototype.fill = function(key, err, data) {
-    var self = this;
-
-    var waiting = self.queues[key];
-    delete self.queues[key];
+    var waiting = this.queues[key];
+    delete this.queues[key];
 
     waiting.forEach(function(task) {
         (task.cb)(err, data);