chore(travis) use yarn

Author: bertho-zero

.travis.yml

@@ -18,16 +18,23 @@ sudo: required
 
 before_install:
   - sudo apt-get -qq update
+  - curl -o- -L https://yarnpkg.com/install.sh | bash
+  - export PATH="$HOME/.yarn/bin:$PATH"
 
 before_script:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
   - export NODE_ENV=development
 
+cache:
+  yarn: true
+  directories:
+    - node_modules
+
 script:
-  - npm run lint
-  - npm test
-  - npm run test-node
+  - yarn lint
+  - yarn test
+  - yarn test-node
 
 env:
   - TRAVIS=travis CXX=g++-4.8