Fix a minor typo in swarm tutorial docs

This fix fixes a minor typo in swarm tutorial's delete service docs.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
(cherry picked from commit 93fa7e75553c3332314b3b988f7082cfde857475)
Signed-off-by: Tibor Vass <tibor@docker.com>

docs/swarm/swarm-tutorial/delete-service.md

@@ -39,5 +39,5 @@ removed the service. The CLI returns a message that the service is not found:
 
 ## What's next?
 
-In the next step of the tutorial, you set up a new service and and apply a
+In the next step of the tutorial, you set up a new service and apply a
 [rolling update](rolling-update.md).