Pin Sphinx.
Pin Sphinx.

Infra advise that 1.2 is bust.

Change-Id: Idd86c1c68c02c06db8a35d2e89f966a8261e8b1e

openstack-infra/reviewstats,openstack-infra/reviewstats,cp16net/reviewstats,JohnGarbutt/reviewstats,JohnGarbutt/reviewstats,cp16net/reviewstats