ClusterStore: fixed incorrect usage of strong-mq

Fixed ClusterStore.publish to publish the message with an empty topic.
The channel name is already stored in the message sent.

This change fixes the problem where sending a message to a channel
"disconnect:{random-id}" crashed the application with assertion error,
because strong-mq does not allow ':' in topic names.

lib/cluster-store.js

@@ -63,7 +63,7 @@ module.exports = function(io) {
       name: name,
       args: args
     };
-    this._pub.publish(data, name);
+    this._pub.publish(data);
   };
 
   /**