Use Node.js version 8 in Travis.

Author: bgaillard

.travis.yml

@@ -8,7 +8,7 @@ php:
   - hhvm
 
 before_install:
-  - curl -sL https://deb.nodesource.com/setup_6.x | sudo -E bash -
+  - curl -sL https://deb.nodesource.com/setup_8.x | sudo -E bash -
   - sudo apt-get install --yes nodejs
   - npm install -g grunt-cli