gitsubmodules: align html and nroff lists

gitsubmodules: align html and nroff lists

There appears to be a bug in the toolchain generating manpages from
lettered lists. When a list is enumerated with letters, the resulting
nroff shows numbers instead. Mostly this is harmless, but in the case of
gitsubmodules, the paragraph following the list refers back to each
bullet by letter. As a result, reading this documentation via `man
gitsubmodules` is hard to parse - readers must infer that a bug exists
and a refers to 1, b refers to 2, and c refers to 3 in the list above.

The problem specifically was introduced in ad47194; previously rather
than generating numerated lists the bulleted area was entirely
monospaced in HTML and shown in plaintext in nroff.

The bug seems to exist in docbook-xml - I've reported it on May 1 via
the docbook-apps mail list - but for now it may make more sense to just
work around the issue.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>