Update CI jobs

gitlab-ci/lint.yml

@@ -1,7 +1,6 @@
 python-linting:
   stage: lint
-  allow_failure: true
-  image: python:3.7.4-slim-stretch
+  image: python:3.7
   before_script:
     - pip install poetry --quiet
     - poetry config cache-dir ~/.cache/poetry
@@ -11,12 +10,19 @@ python-linting:
     - poetry run isort src/ --check-only --recursive
     - poetry run black src/ --line-length 88 --check
     - poetry run autoflake src/ --check --recursive --remove-all-unused-imports --ignore-init-module-imports
+  only:
+    refs:
+      - development
+      - merge_requests
 
 javascript-linting:
   stage: lint
-  allow_failure: true
   image: node:12
   before_script:
     - npm install
   script:
     - npm run lint
+  only:
+    refs:
+      - development
+      - merge_requests