Changed module to service in worker yaml
Changed module to service in worker yaml

As per comments Bookshelf Pub/Sub changelist, I changed "module" to "service" in worker.yaml comments because of change in terminology for Pub/Sub.
wilcoant/bookshelf,GoogleCloudPlatform/getting-started-python,wilcoant/bookshelf,wilcoant/bookshelf,GoogleCloudPlatform/getting-started-python,GoogleCloudPlatform/getting-started-python