Change CI to use Heroku

.gitlab-ci.yml

@@ -16,8 +16,7 @@ test:
 deploy:
   stage: deploy
   script:
-    - systemctl --user stop simple-webapp.service
     - mvn package
-    - systemctl --user start simple-webapp.service
+    - dpl --provider=heroku --app=vs3318-simplewebapp --api-key=$API_TOKEN
   only:
     - master