Update the hogan version

Horizon has moved to hogan 2.0, so we need to as well.

Change-Id: I349d85943fa262d4e077e7c91543b8a2a84de3cb
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Merge pull request #21 from dhellmann/update-hogan

Update the hogan version