org-clock-timestamps-down: Fix typo in docstring

Reported in https://lists.gnu.org/archive/html/bug-gnu-emacs/2021-12/msg01841.html

lisp/org-clock.el

@@ -1747,7 +1747,7 @@ Optional argument N tells to change by that many units."
   (org-clock-timestamps-change 'up n))
 
 (defun org-clock-timestamps-down (&optional n)
-  "Increase CLOCK timestamps at cursor.
+  "Decrease CLOCK timestamps at cursor.
 Optional argument N tells to change by that many units."
   (interactive "P")
   (org-clock-timestamps-change 'down n))