gitlab-ci: reference new docker location

*  .gitlab-ci.yml: here.
3 jobs for master in 6 minutes and 48 seconds
latest
Status Job ID Name Coverage
  Build
passed #48282
build-stable

00:05:18

passed #48283
build-unstable

00:05:29

 
  Publish
passed #48284
dput
publish

00:01:19