Correct link reference in heat/doc
Correct link reference in heat/doc

Currently we are using the new address for api reference. But
heat/doc/source/index.rst still uses the old one.

Change-Id: Ie1423e01a39b1f24fd3fa12368abcb87c8b1ac7c

noironetworks/heat,cwolferh/heat-scratch,noironetworks/heat,cwolferh/heat-scratch,openstack/heat,openstack/heat