feat: Improve build performance by using yarn.

Author: treshugart

init/.travis.yml

@@ -1,16 +1,14 @@
 sudo: false
 language: node_js
 node_js: stable
-cache:
-  directories:
-    - node_modules
 notifications:
   email: false
 before_script:
   - npm prune
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
-  - npm install
+  - npm install -g yarn
+  - yarn install
 script:
   - sk-bundle
   - if [ "<%= "${TRAVIS_SECURE_ENV_VARS}" %>" = "true" ]; then