Bump VERSION to 0.8.0

• Diff: https://gitlab.com/gitlab-org/gitlab-dangerfiles/compare/v0.7.0...e02b57679b8916c446cc53a91fa743f4b5cb18a5

• Release notes:

### New features and features updates

- !17 Introduce a new `Gitlab::Dangerfiles.import_plugins` method.

• 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.