language: node_js
node_js:
- stable
script:
 - npm run lint
 - npm run test
branches:
  only:
  - master
  - /^greenkeeper-/

language: node_js
node_js:
- stable
cache: yarn
script:
 - npm run lint
 - npm run test
branches:
  only:
  - master
  - /^greenkeeper-/

Use yarn cache on CI.
Use yarn cache on CI.

This speeds up the build stage of the CI quite a bit.
