show-branch doc: say <ref>, not <reference>

show-branch doc: say <ref>, not <reference>

The glossary defines 'ref' as the official name of the thing,
and the output from "git grep -e '<ref' Documentation/" shows
that most everybody uses <ref>, not <reference>.  In addition,
the page already says <ref> in its SYNOPSIS section for the
command when it is used in the mode to follow the reflogs.

Strictly speaking, many references of these should be updated to
<commit> after adding an explanation on how these <commit>s are
discovered (i.e. we take <rev>, <glob>, or <ref> and starting from
these commits, follow their ancestry or reflog entries to list
commits), but that would be a lot bigger change I would rather not
to do in this patch, whose primary purpose is to make the existing
documentation more consistent.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Sean Allred <allred.sean@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>