AsciiDoc specification states that in two-line titles, the title
underline has to be the same length as the title text, plus or minus two
characters.  Asciidoctor, however, requires that this must be plus or
minus one character.  Adjust the underlines to be the same length as the
title text to improve compatibility.
Signed-off-by: Nbrian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>