Add install dependencies stage.

.gitlab-ci.yml

@@ -1,7 +1,23 @@
-job_1:
+stages:
-  stage: stage_a
+  - install
+
+install_dependencies:
+  stage: install
   image: node:15-alpine3.10
   tags:
     - docker
   script:
-    - node --version
+    - npm install
+  cache:
+    key:
+      files:
+        - package-lock.json
+    paths:
+      - node_modules
+    policy: pull
+  only:
+    refs:
+      - merge_requests
+      - master
+    changes:
+      - package-lock.json