Add missing word to org-contacts y-or-n-p question

* org-contacts.el (org-contacts-check-mail-address): Add missing word
to y-or-n-p question.

contrib/lisp/org-contacts.el

@@ -388,7 +388,7 @@ This function should be called from `gnus-article-prepare-hook'."
   (let ((mails (org-entry-get (point) org-contacts-email-property)))
     (unless (member mail (split-string mails))
       (when (yes-or-no-p
-             (format "Do you want to this address to %s?" (org-get-heading t)))
+             (format "Do you want to add this address to %s?" (org-get-heading t)))
         (org-set-property org-contacts-email-property (concat mails " " mail))))))
 
 (defun org-contacts-gnus-check-mail-address ()