Use Heroku image for deploy stage

.gitlab-ci.yml

@@ -17,8 +17,6 @@ test:
 
 deploy:
     stage: deploy
-    script:
-      - sudo apt-get update -yq
-      - sudo apt-get install -y ruby-dev
-      - gem install dpl
+    image: heroku/heroku:latest
+    script:  
       - dpl --provider=heroku --app=jlp19-simplewebapp --api-key=$Heroku_API_Key