This makes standard use of shellcheck work without needing to provide extra configuration anywhere.
Also remove use of inline 'shellcheck disable' calls that are already defined in the .shellcheckrc and don't need to be set inline.
The link flag was previously not filtered _after_ fetching build args for dockerfile builds, which meant if a plugin exposed that in it's own docker-args-build trigger, it would break deploys.
Additionally, allow for whitespaces between link and volume flags.
While I do not agree with _every_ style change, this will force Dokku to have consistent formatting across all shell scripts, which is arguably a Good Thing™.
The command used to reprocess everything is:
```shell
shfmt -l -bn -ci -i 2 -w .
```
