Fixed secret creation usage during service create in docs
Using source, the following error is made:
invalid field in secret request: src
@@ -137,7 +137,7 @@ Create a service specifying the secret, target, user/group ID and mode:
```bash
$ docker service create --name redis \
--secret source=ssh-key,target=ssh \
- --secret src=app-key,target=app,uid=1000,gid=1001,mode=0400 \
+ --secret source=app-key,target=app,uid=1000,gid=1001,mode=0400 \
redis:3.0.6
4cdgfyky7ozwh3htjfw0d12qv
```
