Added a rubygems publish task.

This could be tricksy to get right!

.gitlab-ci.yml

@@ -41,3 +41,12 @@ publish:
   script:
     - publish
 
+publish:rubygems:
+  image: $CI_REGISTRY/docker-images/layers:$DISTRO-ruby
+  stage: publish
+  script:
+    - mkdir -p ~/.gem
+    - echo -e "---\n:rubygems_api_key: '$RUBYGEMS_API_KEY'\n"  > ~/.gem/credentials
+    - gem push pkg/jessie/gems/netlinkrb-*.gem
+  only:
+    - master