Fix crash when rendering modeling errors

Oh right, you can't return text from a format.json, but text can be json!

app/controllers/pets_controller.rb

@@ -86,7 +86,7 @@ class PetsController < ApplicationController
       end
       
       format.json do
-        render :text => options[:long_message], :status => options[:status]
+        render :json => options[:long_message], :status => options[:status]
       end
     end
   end