Fix small logo spacing issue

Slightly adjust combo.css so that it doesn't make the OpenStack
logo appear a few pixels too low. This makes the release status
page appear even more like the rest of the status.o.o pages.

Change-Id: I18b779c96e657b6a0b1482b95771670c10a18b6d
Reviewed-on: https://review.openstack.org/30117
Approved: Thierry Carrez <thierry@openstack.org>
Reviewed-by: Thierry Carrez <thierry@openstack.org>
Tested-by: Jenkins