Update .gitlab-ci.yml file

.gitlab-ci.yml

@@ -35,7 +35,8 @@ lint:
     paths:
       - .cache/pip
   before_script :
-    - pip install flake8
+    - mkdir -p .cache/pip
+    - pip install --cache-dir=.cache/pip flake8
   script:
     - echo "Linting Python code.."
     - flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics