Fix typo in order ID - 'DDDD44' to 'DDD44'

PD: I'm in the process of making the Pyladies bot work again and this is really useful! Thanks!

Author: marcorichetta

docs/pretix-client-setup.md

@@ -53,7 +53,7 @@ Order 'BBB22' (paid)
 Order 'CCC33' (paid)
 - Personal Remote Ticket for 'Martina Mustermann'
 
-Order 'DDDD44' (paid)
+Order 'DDD44' (paid)
 - Sponsor Ticket for 'Seán Ó Rudaí'
 - T-Shirt