gitlab-ci: add basic CI

.gitlab-ci.yml

+image: node:latest
+
+stages:
+  - test
+  - build
+
+unit_tests:
+  stage: test
+  script:
+    - npm install
+    - CI=true npm test
+
+build:
+  stage: build
+  script:
+    - npm install
+    - npm run build