ci(xvfb): adds xvfb to run GUI on travis

Author: rahulcs

.travis.yml

@@ -3,8 +3,10 @@ language: node_js
 node_js:
   - "node"
   - "6"
-
-
+before_script:
+  - "export DISPLAY=:99.0"
+  - "sh -e /etc/init.d/xvfb start"
+  - sleep 3 # give xvfb some time to start
 cache:
   directories:
     - node_modules