gitlab: fix build, add nokogiri exception to Gemfile.lock

pkgs/applications/version-management/gitlab/Gemfile.lock

···
   mysql2 (~> 0.3.16)
   net-ssh (~> 3.0.1)
   newrelic_rpm (~> 3.16)
-  nokogiri (~> 1.6.7, >= 1.6.7.2)
+  nokogiri (< 1.6.8, ~> 1.6.7, >= 1.6.7.2)
   oauth2 (~> 1.2.0)
   octokit (~> 4.6.2)
   oj (~> 2.17.4)