Update to the latest ember-dev.

Major new features:

* Automated multi-branch testing for commits with specially formatted
  commit messages (BUGFIX, SECURITY, etc).
* Documentation generator via `rake docs` task.
* Automatic publishing of generated docs for each build.
* Will wait for the Rack server to be ready for connections before
  initiating tests (hopefully mitigates the phantomjs timeout issue)
* Will test each package both with and without feature flags.
* Will abort tests if `defeatureify` is not present and a
  `features.json` file exists.
* Updates to QUnit 1.12.0.
* Updates to use Puma for automated tests.
* Many test improvements.
Merge pull request #3481 from rjackson/update_ember-dev

Update to the latest ember-dev.