specify :select in find to avoid :read_only

The APN::Notification.find call returned read-only ActiveRecords, which
can be prevented by specifying :select.

-> see http://stackoverflow.com/questions/639171/what-is-causing-this-activerecordreadonlyrecord-error

lib/apn_on_rails/app/models/apn/app.rb

@@ -46,7 +46,7 @@ def self.send_notifications_for_cert(the_cert, app_id)
       end
       begin
         APN::Connection.open_for_delivery({:cert => the_cert}) do |conn, sock|
-          notifications = APN::Notification.find(:all, :conditions => conditions, :joins => " INNER JOIN apn_devices ON apn_devices.id = apn_notifications.device_id")
+          notifications = APN::Notification.find(:all, :select => "apn_notifications.*", :conditions => conditions, :joins => " INNER JOIN apn_devices ON apn_devices.id = apn_notifications.device_id")
           notifications.each do |noty|
             conn.write(noty.message_for_sending)
             noty.sent_at = Time.now