The StopPublishing method must have pointer receiver (fixes #34).

publish.go

@@ -212,7 +212,7 @@ func (publisher *Publisher) Publish(
 
 // StopPublishing stops the publishing of messages.
 // The publisher should be discarded as it's not safe for re-use
-func (publisher Publisher) StopPublishing() {
+func (publisher *Publisher) StopPublishing() {
 	publisher.chManager.channel.Close()
 	publisher.chManager.connection.Close()
 }