[PATCH] doc: fix short underline which causes make -C doc to fail

[Kostia Balytskyi]

# HG changeset patch
# User Kostia Balytskyi <ikostia at fb.com>
# Date 1490198110 25200
#      Wed Mar 22 08:55:10 2017 -0700
# Node ID 86383b66465bd7122bb5380047c6e87c888d8227
# Parent  f808c796dfd2c6e4e6990c73a838320512aafeca
doc: fix short underline which causes make -C doc to fail


https://www.mercurial-scm.org/repo/hg-committed/rev/79d98e1b21a7
broke 'make -C doc' by not adding enough underline. This fixes it.

diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -415,7 +415,7 @@ effect and style see :hg:`help color`.
     extension).
 
 ``commands``
-----------
+------------
 
 ``update.requiredest``
     Require that the user pass a destination when running ``hg update``.