Added setup.cfg to make sure the whl file is built for py 2 and 3.
Added setup.cfg to make sure the whl file is built for py 2 and 3.

jazzband/django-constance,APSL/django-constance,metalpriest/django-constance,michaelkuty/django-constance,jerzyk/django-constance,thorgate/django-constance,Andrey86/django-constance,pombredanne/django-constance,askabelin/django-constance,jezdez/django-constance,metalpriest/django-constance,jerzyk/django-constance,winzard/django-constance,jonzlin95/django-constance,dmugtasimov/django-constance,django-leonardo/django-constance,gmflanagan/waterboy,dmugtasimov/django-constance,jazzband/django-constance,jezdez/django-constance,jazzband/django-constance,django-leonardo/django-constance,Andrey86/django-constance,pombredanne/django-constance,thorgate/django-constance,APSL/django-constance,vinnyrose/django-constance,askabelin/django-constance,michaelkuty/django-constance,jonzlin95/django-constance,jmerdich/django-constance,vinnyrose/django-constance,jmerdich/django-constance,winzard/django-constance