Travis: Update node version & chromium invocation

Author: STRML

.travis.yml

@@ -2,11 +2,13 @@ language: node_js
 node_js:
   - "0.10"
   - "0.12"
-  - "4.0"
+  - "4"
+  - "6"
 before_script:
   - export CHROME_BIN=chromium-browser
   - export DISPLAY=:99.0
-  - sh -e /etc/init.d/xvfb start
+  - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -ac -screen 0 1024x768x16"
+  - sleep 3 # give xvfb some time to start
 email:
   on_failure: change
   on_success: never