xfce4-session: update to 4.13.3

Change log:

4.13.3
======
- Reset font-size of logout dialog to default (Bug #15505)
- Report optional dependency on polkit (Bug #12761)
- Read data from correct group when editing autostart entry (Bug
  #10423)
- Improve layout of autostart add/edit dialogs
- Improve column layout of autostart tab (Bug #15448)
- settings: Fix crash when terminating programs (Bug #15489)
- Translation updates:
  Belarusian, Danish, English (Australia), Finnish, French, German,
  Hebrew, Hungarian, Kazakh, Malay, Portuguese, Portuguese (Brazilian),
  Turkish

(gutteridge)