Run Yarn on Travis

Author: simonsmith

.travis.yml

@@ -1,5 +1,5 @@
 language: node_js
-sudo: false
+sudo: required
 node_js:
   - "4"
   - "5"
@@ -8,7 +8,14 @@ addons:
   apt:
     packages:
       - xvfb
+before_install:
+  - 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
+cache:
+  directories:
+  - $HOME/.yarn-cache
 install:
   - export DISPLAY=':99.0'
   - Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
-  - npm install
+  - yarn