Add a .gitlab-ci.yml

Following the instructions[1] for building a jekyll site in gitlab,
I've added this file. Let's see if it works!

[1] https://gitlab.com/pages/jekyll

.gitlab-ci.yml

@@ -0,0 +1,28 @@
+image: ruby:2.3
+
+variables:
+  JEKYLL_ENV: production
+  LC_ALL: C.UTF-8
+
+before_script:
+  - bundle install
+
+test:
+  stage: test
+  script:
+  - bundle exec jekyll build -d test
+  artifacts:
+    paths:
+    - test
+  except:
+  - master
+
+pages:
+  stage: deploy
+  script:
+  - bundle exec jekyll build -d public
+  artifacts:
+    paths:
+    - public
+  only:
+  - master