add alphabetic to lower for consistency (nabijaczleweli)

usr.bin/tr/tr.1

@@ -1,4 +1,4 @@
-.\"	$NetBSD: tr.1,v 1.23 2019/05/29 11:27:34 gutteridge Exp $
+.\"	$NetBSD: tr.1,v 1.24 2021/06/14 17:22:22 christos Exp $
 .\"
 .\" Copyright (c) 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -32,7 +32,7 @@
 .\"
 .\"     @(#)tr.1	8.1 (Berkeley) 6/6/93
 .\"
-.Dd May 29, 2019
+.Dd June 14, 2021
 .Dt TR 1
 .Os
 .Sh NAME
@@ -170,7 +170,7 @@ Class names are:
 .It print	<printable characters>
 .It punct	<punctuation characters>
 .It space	<space characters>
-.It upper	<upper-case characters>
+.It upper	<upper-case alphabetic characters>
 .It xdigit	<hexadecimal characters>
 .El
 .Pp