gitlab: Simplify gitlab-assets build instructions

    buildPhase = ''

      runHook preBuild

      bundle exec rake gettext:compile RAILS_ENV=production NODE_ENV=production

      bundle exec rake rake:assets:precompile RAILS_ENV=production NODE_ENV=production

      bundle exec rake gitlab:assets:compile RAILS_ENV=production NODE_ENV=production

      bundle exec rake gitlab:assets:fix_urls RAILS_ENV=production NODE_ENV=production

      bundle exec rake gitlab:assets:check_page_bundle_mixins_css_for_sideeffects RAILS_ENV=production NODE_ENV=production

      bundle exec rake gitlab:assets:compile RAILS_ENV=production NODE_ENV=production SKIP_YARN_INSTALL=true

      runHook postBuild

    '';