Fix latest doc error
Fix latest doc error

Until fix [1] lands, people should learn to install
a git hook or do tox -edocs before posting a review

[1] https://review.openstack.org/#/c/229951/

Change-Id: I37e50c2d018b6ac67f2792c29eab0081afa16d75

MaximNevrov/neutron,cloudbase/neutron,huntxu/neutron,sebrandon1/neutron,sebrandon1/neutron,igor-toga/local-snat,cloudbase/neutron,wolverineav/neutron,openstack/neutron,bigswitch/neutron,mahak/neutron,MaximNevrov/neutron,igor-toga/local-snat,noironetworks/neutron,openstack/neutron,noironetworks/neutron,eayunstack/neutron,wolverineav/neutron,eayunstack/neutron,klmitch/neutron,mahak/neutron,klmitch/neutron,openstack/neutron,mahak/neutron,huntxu/neutron,bigswitch/neutron