Bump version to 6.14.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v6.13.0...1eccdba80b1c8dd61593dc2c1ab92a1b1d24a600

• Release notes:

### Fixes

- !599 Use `GITLAB_CI_API_TOKEN` against `CI_API_V4_URL` for querying failed jobs

• Checklist before merging:

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

• Checklist after merging:

  • Create a tag for the new release version.