fix double service name

Signed-off-by: Alexander Ryabov <i@sepa.spb.ru>

docs/reference/commandline/service_update.md

@@ -203,7 +203,7 @@ The following example adds a new alias name to an existing service already conne
 ```bash
 $ docker service update \
   --network-rm my-network \
-  --network-add name=my-network,alias=web1 my-web \
+  --network-add name=my-network,alias=web1 \
   myservice
 ```