ox-icalendar: Fix timezone export bug

* ox-icalendar.el (org-icalendar-export-current-agenda): Correct
  argument order in call to org-icalendar--vcalendar (timezone should be
  third, description fourth).

TINYCHANGE

lisp/ox-icalendar.el

@@ -909,8 +909,8 @@ This function assumes major mode for current buffer is
        (org-icalendar--vcalendar
 	org-icalendar-combined-name
 	user-full-name
-	org-icalendar-combined-description
 	(or (org-string-nw-p org-icalendar-timezone) (cadr (current-time-zone)))
+	org-icalendar-combined-description
 	contents)))
     (run-hook-with-args 'org-icalendar-after-save-hook file)))