Bump version to 5.4.2

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v5.4.1...508695d9f943afb11ca274ee65714f24f11897ee

• Release notes:

### Fixes

- !423 Report from gitlab-qa-mirror as master

### Doc changes

- !420 Adding documentation for maven orchestrated spec

• 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.