Use xvfb as a service.

Author: dblock

.travis.yml

@@ -7,13 +7,12 @@ cache: bundler
 
 services:
   - mongodb
+  - xvfb
 
 addons:
   firefox: 54.0
 
 before_install:
-  - export DISPLAY=:99.0
-  - sh -e /etc/init.d/xvfb start
   - wget https://github.com/mozilla/geckodriver/releases/download/v0.18.0/geckodriver-v0.18.0-linux64.tar.gz
   - mkdir geckodriver
   - tar -xzf geckodriver-v0.18.0-linux64.tar.gz -C geckodriver