Added missing backslash to documentation sites cli snippet
I think the cli code block misses a backslash to brevent line break when copy/pasting it to a terminal.
I doubt that this is intentional, if it is, feel free to reject the pr.
@@ -291,7 +291,7 @@ service with two labels:
```console
$ docker service create \
--name redis_2 \
- --label com.example.foo="bar"
+ --label com.example.foo="bar" \
--label bar=baz \
redis:3.0.6
```
