Update .gitlab-ci.yml

.gitlab-ci.yml

 image: ruby:2.3
 
-cache:
-  paths:
-  - vendor/
+variables:
+  JEKYLL_ENV: production
 
 before_script:
-  - bundle install --path vendor
+  - bundle install
 
+test:
+  stage: test
+  script:
+  - bundle exec jekyll build -d test
+  artifacts:
+    paths:
+    - test
+  except:
+  - master
+  
 pages:
   stage: deploy
   script:
@@ -15,14 +24,5 @@ pages:
     paths:
     - public
   only:
-  - master
+  - gh-pages
 
-test:
-  stage: test
-  script:
-  - bundle exec jekyll build -d test
-  artifacts:
-    paths:
-    - test
-  except:
-  - master
\ No newline at end of file