A recent update in [GitLab UI] and setting the [config.assets.paths] to
include `node_modules` for the resolution of SCSS imports, allows us to
have much nicer imports which don't rely on brittle relative paths.

This change also forwards @gitlab/ui to the newest version

[GitLab UI]: https://gitlab.com/gitlab-org/gitlab-ui/merge_requests/602
[config.assets.paths]: https://gitlab.com/gitlab-org/gitlab-ce/blob/d9026d0ffa0/config/application.rb#L169