chore: add lint script

Closes #3 (closed)

.gitlab-ci.yml

@@ -9,3 +9,13 @@
         - yarn
     script:
         - yarn lint
+
+build:
+    stage: checks
+    before_script:
+        - yarn
+    script:
+        - cd packages/ra-cubicweb
+        - yarn build
+        - cd ../demo
+        - yarn build