[Trivial] Correct a typo in the docs
[Trivial] Correct a typo in the docs

Follow-up to 08b5bd725a523f4458ada0d49a2e2dfd5ca20e02.

Change-Id: Id788c115e47ff40b2ecfcb078419c39304a120a3

openstack/bifrost,openstack/bifrost