Add CentOS 7 to tested platforms
Add CentOS 7 to tested platforms

This one-line change is an assertion that Rundeck has been installed and
is functional on CentOS 7.  Since CentOS 7 is already included in the
supported platforms, this change is merely to keep documentation up to
date.

voxpupuli/puppet-rundeck,danifr/puppet-rundeck,cy4n/puppet-rundeck,DevOpsFu/puppet-rundeck,dalisch/puppet-rundeck,tkwilliams/puppet-rundeck,cernops/puppet-rundeck,cernops/puppet-rundeck,jyaworski/puppet-rundeck,jyaworski/puppet-rundeck,dandunckelman/puppet-rundeck,puppet-community/puppet-rundeck,dalisch/puppet-rundeck,danifr/puppet-rundeck,DevOpsFu/puppet-rundeck,bodhi-space/puppet-rundeck,fairfaxmedia/puppet-rundeck,zlanyi/puppet-rundeck,bodhi-space/puppet-rundeck,dandunckelman/puppet-rundeck,cy4n/puppet-rundeck,zlanyi/puppet-rundeck,fairfaxmedia/puppet-rundeck,tkwilliams/puppet-rundeck,puppet-community/puppet-rundeck,voxpupuli/puppet-rundeck