bug#34596: Typo in regex-opt doc string

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Wed, 20 Feb 2019 23:10:52 +0100
> 
>  (defun simplified-regexp-opt (strings &optional paren)
>    (let ((parens
>           (cond ((stringp paren)       (cons paren "\\)"))
>                 ((eq paren 'words)    '("\\<\\(" . "\\)\\>"))
>                 ((eq paren 'symbols) '("\\_<\\(" . "\\)\\_>"))
>                 ((null paren)          '("\\(?:" . "\\)"))
>                 (t                       '("\\(" . "\\)")))))
>      (concat (car paren)
>              (mapconcat 'regexp-quote strings "\\|")
>              (cdr paren))))
> 
> `paren' should be `parens'  in the last three lines.

Thanks, fixed.