Update gitlab CI

Add flake8 and black

depends on !35 (merged)

.gitlab-ci.yml

@@ -14,7 +14,7 @@ before_script:
   - python --version
   - python3 -m venv venv
   - source venv/bin/activate
-  - pip install black==22.3.0 flake8==4.0.1
+  - pip install black==22.3.0 flake8==4.0.1 pylint==2.13.8
 
 stages:
   - lint
@@ -32,3 +32,10 @@ flake8:
   stage: lint
   script:
     - flake8 .
+
+pylint:
+  tags:
+    - lint
+  stage: lint
+  script:
+    - pylint app *.py