Set up xvfb on travis

Author: jurre

.travis.yml

@@ -1,3 +1,4 @@
+dist: trusty
 rvm:
 - 2.4.2
 bundler_args: "--without debug development"
@@ -9,5 +10,6 @@ before_script:
 - export SECRET_KEY_BASE="$(bundle exec rake secret)"
 - cp config/database.travis.yml config/database.yml
 - psql -c 'create database hours_test' -U postgres
-- export DISPLAY=:99.0
-- sh -e /etc/init.d/xvfb start
+- "export DISPLAY=:99.0"
+- "sh -e /etc/init.d/xvfb start"
+- sleep 3 # give xvfb some time to start