Try starting xvfb through services

It seems the default Travis builds run on Xenial now instead of Trusty.

https://docs.travis-ci.com/user/gui-and-headless-browsers/#using-services

.travis.yml

@@ -16,6 +16,9 @@ matrix:
       env: LARAVEL='5.8.*'
   fast_finish: true
 
+services:
+  - xvfb
+
 addons:
   chrome: stable
 
@@ -30,8 +33,6 @@ before_script:
   - if [[ $COVERAGE == "" ]]; then phpenv config-rm xdebug.ini; fi
   - composer config discard-changes true
   - ./vendor/bin/dusk-updater update
-  - export DISPLAY=:99.0
-  - sh -e /etc/init.d/xvfb start
   - ./vendor/laravel/dusk/bin/chromedriver-linux &
   - google-chrome-stable --headless --disable-gpu --remote-debugging-port=9222 http://localhost &