devstack: Fix requirement typo
devstack: Fix requirement typo

Change-Id: Idc02b2fc75e26880544207563825f9f5ccbaa77b

sileht/gnocchi,sileht/gnocchi,leandroreox/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi,gnocchixyz/gnocchi