install grunt-cli globally

Author: Bogdan Livadariu

.travis.yml

@@ -12,6 +12,7 @@ install:
   - npm set progress=false
   - travis_retry npm install
 before_script:
+  - npm install -g grunt-cli
   - 'export DISPLAY=:99.0'
   - 'sh -e /etc/init.d/xvfb start'
 script: