Update .gitlab-ci.yml (#36)

Author: sepehr-rs

.gitlab-ci.yml

@@ -12,4 +12,18 @@ pages:
       - public
 
   only:
-    - main
+    - main
+
+check_lockfile:
+  image: node:lts
+  stage: test
+  script:
+    - npm ci
+    - npm install --package-lock-only
+    - |
+      if ! git diff --quiet package-lock.json; then
+        echo "package-lock.json is out of date. Run 'npm install' and commit the changes."
+        exit 1
+      fi
+  only:
+    - main