Bump to Ruby 2.3

.gitlab-ci.yml

@@ -1,6 +1,6 @@
+image: ruby:2.3
+
 pages:
-  stage: deploy
-  image: ruby:2.1
   script:
   - gem install jekyll
   - jekyll build -d public
@@ -8,4 +8,4 @@ pages:
     paths:
     - public
   only:
-  - master
+  - master