fix export large set of bulletin overflow issue

app/controllers/admin/announcements_controller.rb

@@ -186,7 +186,7 @@ class Admin::AnnouncementsController < OrbitAdminController
       end
       Thread.new do
         begin
-          @announcements = Bulletin.all.desc(:created_at)
+          @announcements = Bulletin.all.desc(:id)
           last_updated = [Bulletin.max(:updated_at).to_i, AnnouncementSetting.max(:updated_at).to_i].max
           filename = "public/announcement_export_#{last_updated}.xlsx"
           if File.exist?(filename)