Bump VERSION to 1.1.1

• Diff: https://gitlab.com/gitlab-org/gitlab-dangerfiles/compare/v1.1.0...c6f86cac03768831d83b121890f977201b0d967d

• Release notes:

### Fixes

- !31 Don't require Helper from Roulette to avoid Danger failing in `Danger#validate_file_contains_plugin!`.

### Other changes (tooling, technical debt)

- !28 Move plugin files under `danger/plugins`.
- !30 Use `gitlab_helper.mr_changes` instead of performing the API call ourselves.

• Checklist before merging:

  • Diff link is up-to-date.
  • Based on the diff, lib/gitlab/dangerfiles/version.rb is updated, according to SemVer.
  • Release notes are accurate.

• Checklist after merging:

  • Update the release notes for the newly created tag.