node_config -> CONFIG -> config.js -> config

.gitlab-ci.yml

 image: node:7
 
-before_script:
-  - curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
-  - echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
-  - sudo apt-get update && sudo apt-get install yarn
+before_script
+  - npm install -g yarn:
   - yarn
 
 test: