fix Rails::Engine namespace

Author: Fivell

lib/active_admin_sidebar.rb

@@ -4,14 +4,14 @@
 require 'active_admin_sidebar/positions'
 
 module ActiveAdminSidebar
-  module  Rails
-  class Engine < Rails::Engine
+  module Rails
+    class Engine < ::Rails::Engine
       config.after_initialize do
-          ActiveAdmin::BaseController.send :include, ActiveAdminSidebar::Positions
+        ActiveAdmin::BaseController.send :include, ActiveAdminSidebar::Positions
       end
+    end
   end
 end
-end