Update to Ember 1.4.0-beta.2.

Ember 1.3 does not properly normalize the looked up template/route names. This
causes loading and error states to not work under our updated resolver (since
we rely on path normalization).

For reference:

https://github.com/stefanpenner/ember-jj-abrams-resolver/issues/13
https://github.com/stefanpenner/ember-app-kit/issues/427
https://github.com/stefanpenner/ember-app-kit/issues/428