Collapse extended into the base centos-ruby image...
Without some of the packages currently being installed by extended,
any gem that requires native extensions will fail the bundle install.
Moving extended into the main image so that the main image covers
the 80% use case.

Also fixing puma startup, since we are running the server from the
APP_ROOT already, puma doesn't need it specified in the conf.
Merge pull request #25 from jwforres/collapse_extended_ruby_to_base

Collapse extended into the base centos-ruby image...