Bump VERSION to 0.6.0

• Diff: https://gitlab.com/gitlab-org/gitlab-dangerfiles/compare/v0.5.0...2e578c2

• Release notes:

### New features and features updates

- !11 Update various files with gitlab-org/gitlab latest changes.

• 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.