Rebuild Passenger/Nginx when Ruby version changes.

When a new version of Ruby is installed, all the system gems are also reinstalled. The new installation of the Passenger gem does not have the Nginx module. Previously rubber:passenger_nginx:custom_install did not detect this and did not rebuild the missing Nginx module.
Merge pull request #436 from willkoehler/deploy_passenger_nginx_fix

Rebuild Passenger/Nginx when Ruby version changes.