Fixed multiple application notifications

When there were multiple applications set up, all notifications were
sent as if belong to the first one.

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

@@ -40,7 +40,7 @@ def self.send_notifications
   def self.send_notifications_for_cert(the_cert, app_id)
     begin
       APN::Connection.open_for_delivery({:cert => the_cert}) do |conn, sock|
-        unset = APN::Notification.where(:sent_at => nil).order(:device_id, :created_at)
+	unset = APN::Notification.joins(:device).where(:sent_at => nil, :apn_devices => { :app_id => app_id }).order(:device_id, :created_at)
         unset.each do |noty|
           Rails.logger.debug "Sending notification ##{noty.id}"
           begin