Maintenance release 🔧
- move CI from travis to GH actions
- bump minimum required ruby version to 2.6.0 (same as Wordmove)
- reintroduced rubocop (in CI too) and fixed all the code as per its notes
- update dependencies
A lot of kudos go to @korkey128k for his original PR #22. Thanks to updated dependencies Photocopier now should be able to fully support ed25519 ssh keys.