rails/jbuilder — pull request #12 by whitequark (2012-01-23 09:09:59+00:00)
Title: Use Mime::JSON as the default response type

Other template builders ([e.g. XML](https://github.com/rails/rails/blob/master/actionpack/lib/action_view/template/handlers/builder.rb)) set their default format. Make jbuilder consistent with that.