tox: fix doc8 command in py27
tox: fix doc8 command in py27

Change-Id: I1b793e0de5145c9dc0c8023d904dce5bef2cc992

gnocchixyz/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,sileht/gnocchi,leandroreox/gnocchi,idegtiarov/gnocchi-rep,idegtiarov/gnocchi-rep,leandroreox/gnocchi,idegtiarov/gnocchi-rep