org-clock: Fix compilation error

Reported-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
<http://lists.gnu.org/archive/html/emacs-orgmode/2017-09/msg00623.html>

lisp/org-clock.el

@@ -2974,6 +2974,7 @@ The details of what will be saved are regulated by the variable
 
 ;; Local variables:
 ;; generated-autoload-file: "org-loaddefs.el"
+;; coding: utf-8
 ;; End:
 
 ;;; org-clock.el ends here