Update programming language mentioned in setup.cfg
Update programming language mentioned in setup.cfg

As py35 has been dropped and py36, py37 jobs are running, so
updated the setup.cfg accordingly.

Change-Id: I85af2a9116d9b15a4fa6b35cb562f4de277a828f

stackforge/kolla,rahulunair/kolla,stackforge/kolla,openstack/kolla,openstack/kolla,stackforge/kolla,rahulunair/kolla