Ensure jj-abrams ember-data is used.

Rubygems by default was using `0.14` since it was not marked as a
beta/pre-release version. This is a HORRIBLE thing since the generators
in ember-rails expect specific changes from the reboot (e.g.
ActiveModelAdapter).
Merge pull request #332 from rjackson/ensure_recent_ember_data

Ensure jj-abrams ember-data is used.