Fix For Ember Projects Not In Root Directory

If you have a project structure such that the Ember application is not in the root directory, [this line](https://github.com/KatalysatorAB/atom-ember-tabs/blob/16994efe33616e6fb46e8432f79b9d49ec88e06a/lib/ember-pods-project.coffee#L18) fails. Would it be possible to search for a file named `.ember-cli` instead of assuming it is in the root directory?
