this solves mqtt publishing bug

#1274 bug  fix

app/models/agents/mqtt_agent.rb

@@ -109,7 +109,7 @@ module Agents
     def receive(incoming_events)
       mqtt_client.connect do |c|
         incoming_events.each do |event|
-          c.publish(interpolated(event)['topic'], event)
+          c.publish(interpolated(event)['topic'], event.payload)
         end
       end
     end