constrain Ruby version from 1.9.3 > p0 to 2.0.0

added RedCard as a dependency

Its tough for regular users to appreciate the new user experience. People trying to use 1.9.3p0 and 2.1.0 are common.

See also:
- https://github.com/cloudfoundry/bosh/pull/569
- https://www.pivotaltracker.com/s/projects/956238/stories/67369232