Option to allow for no files

[leighhalliday]

We use erb-lint in a pre-commit hook and in our CI. Sometimes files have changed (ie. in git diff) which are excluded from our erb-lint checks. This causes an error of no files found... to be output, which doesn't allow the commit to take place.

We have workarounds in place:

git diff HEAD^ --name-only --diff-filter=d -m **/*.erb | xargs --no-run-if-empty bundle exec erblint 2> error_output || [ "$(cat error_output)" == "no files found..." ]

And:

PAGER=cat git diff --diff-filter=d --name-only --cached -- "*.erb" | xargs bundle exec erblint 2> /tmp/erblint; (( erblint_status = $? ))

# No files found are treated as an error, let's treat it as success
if [[ "$(cat /tmp/erblint)" == "no files found..." ]]; then
  erblint_status=0
fi

But having a --allow-no-files option would let us treat this as a successful check without additional logic for this scenario.