We have to do this in order to ensure that an updated .gitlab-ci.yml is actually available on every release.

We do a release every day so we end up with a lot of "release commits"
(noise) in the master branch, which we don't want.

Add base-devel tag

Closes #35

See merge request archlinux/archlinux-docker!39

We can simply construct it ourselves.

This is expected of the new generic package API:
https://docs.gitlab.com/ee/user/packages/generic_packages/