Update .gitlab-ci.yml

backend/secfit/.gitlab-ci.yml

 build:
   stage: build
   script:
-    - apt-get add postgresql-dev --no-cache
+    - apt-get clean
     - pip install -r backend/secfit/requirements.txt
+  cache:
+      paths:
+        - ~/.cache/pip/
+  services:
+    - postgres:latest
 
 deploy:
-  stage: deploy
-  image: python:3.8.5-slim
   script:
-    - git remote add heroku https://heroku:$HEROKU_API_KEY@git.heroku.com/secfit-group15.git
-    - git push heroku master
-    - echo "Deployed to Staging Server https://secfit-group15.herokuapp.com"
-  environment:
-    name: staging
-    url: https://secfit-group15.herokuapp.com/
+    - apt-get update -qy --allow-insecure-repositories
+    - apt-get install -y ruby-dev
+    - apt-get install git -yqq
+    - apt-get install curl -y
+    - gem install dpl
+    - dpl --provider=heroku --app=tdt4242-backend --api-key=$HEROKU_API_KEY --skip_cleanup
   only:
     - master