Better missing `secret_key_base` error message

Previously the error was:

```
RuntimeError: You must set secret_key_base in your app's config
```

Will now be:


```
RuntimeError: Missing `secret_key_base` for 'production' environment, set this value in `config/secrets.yml`
```
Merge pull request #13471 from schneems/schneems/better-secrets-error-message

Better missing `secret_key_base` error message