Add Yarn as a build dependency

Add the latest version of Yarn. We are going to use it instead of npm our javascript dependancy management.

Closes: https://gitlab.com/gitlab-org/gitlab-omnibus-builder/issues/6

assigned to @marin

added 1 commit

• 4d6ea977 - I don't see distcc available in any opensuse 13.2 repos

Compare with previous version

mentioned in merge request omnibus-gitlab!1315 (merged)

mentioned in commit 4b207a0c

merged

mentioned in merge request gitlab-development-kit!275 (merged)

mentioned in issue gitlab-development-kit#221 (closed)