Fix pygments style
Fix pygments style

New theme of docs respects pygments_style.

more info: http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014971.html

Change-Id: Ifc0f70adf3a426314ff6df41c58b6aa5aeca17fb

openstack/rally,openstack/rally,openstack/rally,openstack/rally