let rake task use orbit site's environment

lib/tasks/bulletin_tasks.rake

@@ -1,7 +1,7 @@
 desc 'Remove duplicated bulletins (announcements) created by preview'
 
 namespace :bulletin do
-  task :remove_preview_bulletins do
+  task :remove_preview_bulletins => [:environment] do
     bulletins = Bulletin.where(is_preview: true)
     bulletins.destroy_all
   end