Revert "[CHORES] Use custom Docker image to pylint job"

This reverts commit 39a9a0e3.

.gitlab-ci.yml

@@ -4,8 +4,10 @@ stages:
   - deploy
 
 pylint:
-  image: farhanazmi/digipus
+  image: python:3.7
   stage: test
+  before_script:
+    - pip install -r requirements.txt
   script:
     - mkdir ./pylint
     - git ls-files | grep -v 'migrations' | grep -v 'settings.py' | grep -v 'manage.py' | grep -E '.py$' | xargs pylint -E --load-plugins=pylint_django --output-format=text --score=yes | tee ./pylint/pylint.log || pylint-exit $?