Require gear 0.3.1.

And less than 0.4.0 for safety.

Change-Id: I539a2cc7816c15491db55975ac07ee7a148535dc
Reviewed-on: https://review.openstack.org/32973
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins