Use underscore module name in route scope

Rails 4 breaks with camel case module name.
Still works under Rails 3.

config/routes.rb

@@ -1,6 +1,6 @@
 #DeviseHeroku::Engine.routes.draw do
 Rails.application.routes.draw do
-  scope :module => "DeviseHeroku" do
+  scope :module => "devise_heroku" do
     post "/heroku/sso/login" => "sso#login"
   end
 end