Monkey patch ember-cli's Builder.prototype.build.

This fixes an issue with the ember-cli Builder.prototype.build
implementation for 0.1.3 and 0.1.4. The bug was fixed in
https://github.com/stefanpenner/ember-cli/pull/2792 and will be
availabe in 0.1.5.  Once that version is published and in normal
usage this monkey patch can be removed.