Update examples in README: change Wily to Xenial
Update examples in README: change Wily to Xenial

Wily is no longer supported.

phusion/passenger_apt_automation,phusion/passenger_apt_automation,phusion/passenger_apt_automation,phusion/passenger_apt_automation,phusion/passenger_apt_automation,phusion/passenger_apt_automation,phusion/passenger_apt_automation