Fixed missing async for function on

Author: Seluj78

docs/source/rabbitmq-tutorial/examples/2-work-queues/worker.py

@@ -4,7 +4,7 @@
 loop = asyncio.get_event_loop()
 
 
-def on_message(message: IncomingMessage):
+async def on_message(message: IncomingMessage):
     async with message.process():
         print(" [x] Received message %r" % message)
         print("     Message body is: %r" % message.body)