Add Rails asset pipeline directories to spec pipeline

That way, you can require JS files loaded from gems, etc.

For example, if you want to include “angular-mocks.js” from the
angularjs-rails gem, you can make a file in spec/javascripts/helpers
with a `//= require angular-mocks` Sprockets directive.
Merge pull request #211 from nertzy/add-vendor-assets-to-spec-pipeline

Add application asset directories to spec pipeline