Add lint (using rubocop) job to the CI

.gitlab-ci.yml

@@ -1,9 +1,21 @@
 stages:
-    - setup
+    - lint
     - build
     - checking
     - deploy
 
+run-lint:
+  image: debian:stable
+  stage: lint
+  allow_failure: true
+  tags:
+    - debian
+  before_script:
+    - apt-get update
+    - apt-get install -y rubocop
+  script:
+    - rubocop
+
 # Build package using dpkg-buildpackage
 run-build:
     stage: build