Start 'xvfb' service on new Travis' xenial
Start 'xvfb' service on new Travis' xenial

Travis switched us to the xenial dist for free and automatically. Following
their docs https://docs.travis-ci.com/user/gui-and-headless-browsers/#using-xvfb-to-run-tests-that-require-a-gui
we have to change how we start 'xvfb'

SublimeLinter/SublimeLinter3,SublimeLinter/SublimeLinter3