org-icalendar.el (org-icalendar-ts-to-string): Fix bug in converting timezone

org-icalendar.el (org-icalendar-ts-to-string): Fix bug in converting
timezone.

TINYCHANGE

lisp/org-icalendar.el

@@ -677,7 +677,7 @@ a time), or the day by one (if it does not contain a time)."
       (setq fmt (if have-time
 		    (replace-regexp-in-string "%Z"
 					      org-icalendar-timezone
-					      org-icalendar-date-time-format)
+					      org-icalendar-date-time-format t)
 		  ";VALUE=DATE:%Y%m%d"))
       (concat keyword (format-time-string fmt time
 					  (and (org-icalendar-use-UTC-date-timep)