Use a railtie for Audited::Sweeper's ActiveSupport.on_load hook

This prevents loading ActionController::API before Rails itself has
loaded it.

lib/audited.rb

@@ -30,3 +30,4 @@ def config
 ::ActiveRecord::Base.send :include, Audited::Auditor
 
 require 'audited/sweeper'
+require 'audited/railtie'

lib/audited/railtie.rb

@@ -0,0 +1,14 @@
+module Audited
+  class Railtie < Rails::Railtie
+    initializer "audited.sweeper" do
+      ActiveSupport.on_load(:action_controller) do
+        if defined?(ActionController::Base)
+          ActionController::Base.around_action Audited::Sweeper.new
+        end
+        if defined?(ActionController::API)
+          ActionController::API.around_action Audited::Sweeper.new
+        end
+      end
+    end
+  end
+end

lib/audited/sweeper.rb

@@ -38,12 +38,3 @@ def controller=(value)
     end
   end
 end
-
-ActiveSupport.on_load(:action_controller) do
-  if defined?(ActionController::Base)
-    ActionController::Base.around_action Audited::Sweeper.new
-  end
-  if defined?(ActionController::API)
-    ActionController::API.around_action Audited::Sweeper.new
-  end
-end

spec/audited/sweeper_spec.rb

@@ -30,6 +30,7 @@ def populate_user; end
   render_views
 
   before do
+    Audited::Railtie.initializers.each(&:run)
     Audited.current_user_method = :current_user
   end