machine:
  node:
    version: 6.9

test:
  override:
    - nvm install 6.8 && npm rebuild && npm test
    - nvm install 7.1 && npm rebuild && npm test
    - nvm install 7.2 && npm rebuild && npm test
    - nvm install 4 && npm rebuild && npm test

machine:
  node:
    version: 6

test:
  override:
    - npm test
    - nvm install 7 && npm rebuild && npm test
    - nvm install 4 && npm rebuild && npm test

Test on 4.x, 6.x and 7.x
Test on 4.x, 6.x and 7.x