bgpwtf/invoice: bump for 2020

This doesn't automatically bump generated numbers - however, new users
will at least have sensible IDs now :).

To bump an existing deployment, you will have to do some mild surgery:

 - edit the touched query to once generate a new, appropriate serial
   (eg. 20001)
 - run and seal one invoice
 - restore original code (now with the new 20000 default)

In the future we should have an RPC override for the new sealed final
UID with some basic sanity checks.

Change-Id: Idd8187618869f6ea76f1b187acfbdd2f1c94005b
diff --git a/bgpwtf/invoice/model.go b/bgpwtf/invoice/model.go
index 1fb89b9..fcf4aba 100644
--- a/bgpwtf/invoice/model.go
+++ b/bgpwtf/invoice/model.go
@@ -75,11 +75,11 @@
 			invoice_id, final_uid, sealed_time
 		) values (
 			?,
-			( select printf("%04d", ifnull( (select final_uid as v from invoice_seal order by final_uid desc limit 1), 19000) + 1 )),
+			( select printf("%04d", ifnull( (select final_uid as v from invoice_seal order by final_uid desc limit 1), 20000) + 1 )),
 			?
 		)
-
 	`
+
 	sealTime := time.Now()
 	if useProformaTime {
 		sealTime = time.Unix(0, invoice.Date)