Three hyphens are rendered verbatim in documentation, so "--" has to be
used to produce a dash. Fix asciidoc output for dashes. This is
similar to previous commits f0b922473e (Documentation: render special
characters correctly, 2021-07-29) and de82095a95 (doc
hash-function-transition: fix asciidoc output, 2021-02-05).
Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
