use a beta release of ember-data

Use a beta release of ember-data until a stable release of ember-data
is published. Otherwise, users get a 404 with the defaults.
Merge pull request #319 from fivetanley/use-beta-for-ember-data

use a beta release of ember-data
Whitespace cleanup.
Fix typo.
Change status to warning when defaulting to Ember Data beta channel.
Bump version.
Update README.md
Merge pull request #322 from JFickel/patch-1

Update README.md