Fix secrets related info in Deployment docs (#3406)
Fix secrets related info in Deployment docs (#3406)

I guess it is a typo, as it is generally bad idea to commit secrets to vcs and `config/prod.secret.exs` itself mentions it:

```
# ... You can also
# hardcode secrets, although such is generally not
# recommended and you have to remember to add this
# file to your .gitignore
```
optikfluffel/phoenix,nshafer/phoenix,phoenixframework/phoenix,optikfluffel/phoenix,optikfluffel/phoenix,Gazler/phoenix,rafbgarcia/phoenix,0x00evil/phoenix,eksperimental/phoenix,michalmuskala/phoenix,rafbgarcia/phoenix,rafbgarcia/phoenix,phoenixframework/phoenix,0x00evil/phoenix,nshafer/phoenix,eksperimental/phoenix,keathley/phoenix,Gazler/phoenix,jwarwick/phoenix,michalmuskala/phoenix,nshafer/phoenix,phoenixframework/phoenix,jwarwick/phoenix,keathley/phoenix,0x00evil/phoenix