ci(travis): run tests for osx, linux, & windows

.travis.yml

@@ -1,15 +1,6 @@
 language: node_js
 sudo: false
-node_js:
- - '6'
- - '8'
- - 'lts/*'
- - 'node'
-os:
- - linux
- - osx
-env:
- - FORCE_COLOR=true
+env: FORCE_COLOR=true
 
 # Trigger a push build on master and greenkeeper branches + PRs build on every branches
 # Avoid double build on PRs (See https:/travis-ci/travis-ci/issues/1147)
@@ -26,6 +17,21 @@ script:
 
 jobs:
  include:
+ - stage: test
+ node_js: '6'
+ os: osx
+ - node_js: '8'
+ os: osx
+ - os: linux
+ node_js: 'lts/*'
+ # uncomment in the future when this is fixed: https://travis-ci.community/t/node-js-build-fails-with-no-obvious-error/961/8
+ #- os: windows
+ # node_js: 'lts/*'
+ - os: osx
+ node_js: 'lts/*'
+ # latest version of node
+ - node_js: 'node'
+ os: osx
  - stage: release
  node_js: lts/*
  script: