Fix Wikidata birthday detection

Authored by Lucas_Werkmeister_WMDE on Thu, Nov 23, 1:52 PM.

Description

Fix Wikidata birthday detection

In JavaScript, months are numbered starting from 0, so we need to
*subtract* one from the usual month number to get the right one for the
Date constructor, not add one! (Without this fix, birthday presents are
only enabled on *December* 29th.)

Change-Id: I83c3b9dad3b02ebac0b5cbd6be347ddc15eac61f