command "docker service remove" not insistant

Signed-off-by: lixiaobing10051267 <li.xiaobing1@zte.com.cn>

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

@@ -20,7 +20,7 @@ you can delete the service from the swarm.
 run your manager node. For example, the tutorial uses a machine named
 `manager1`.
 
-2. Run `docker service remove helloworld` to remove the `helloworld` service.
+2. Run `docker service rm helloworld` to remove the `helloworld` service.
 
     ```
     $ docker service rm helloworld