Update to Ember 1.3.1

Fixes security issues:

* [CVE-2014-0013](https://groups.google.com/forum/#!topic/ember-security/2kpXXCxISS4)
* [CVE-2014-0014](https://groups.google.com/forum/#!topic/ember-security/PSE4RzTi6l4)

Blog post:

http://emberjs.com/blog/2014/01/14/ember-security-releases.html
Merge pull request #1024 from rjackson/update_ember

Update to Ember 1.3.1