doc/org.texi: Fix wrong date in example.

doc/org.texi

@@ -4572,7 +4572,7 @@ in @b{bold}.
 14            --> @b{2006}-@b{06}-14
 12            --> @b{2006}-@b{07}-12
 Fri           --> nearest Friday (defaultdate or later)
-sep 15        --> @b{2006}-11-15
+sep 15        --> @b{2006}-09-15
 feb 15        --> @b{2007}-02-15
 sep 12 9      --> 2009-09-12
 12:45         --> @b{2006}-@b{06}-@b{13} 12:45