fedora-git-commit-mail-hook: Fix command for finding previous tag

[Jeremy Katz]

On Monday, June 22 2009, Todd Zullinger said:
[snip]
> I think we may want to look at converting from our use of the update
> hook to the post-receive hook for sending commit notifications.
> Upstream moved the mail notification bits from the update hook to a
> new post-receive hook only a few weeks after Jeremy added the initial
> fedora-git-commit-mail-hook.  So what we're running now isn't
> something which will receive any attention or bug fixes from upstream,
> unfortunately.  The reasoning for upstream moving mail notification is
> stated in the the commit message for 46d409d:

That sounds sensible.  I have no problem with us changing, although I
won't have the time to sit down and make it happen any time in the next
couple of weeks.  If someone can get to it before, I'm more than happy
to look over it.

Alternately, I can stick on my queue for July :)

Jeremy