[tests] Use flake8 and isort versions defined in openwisp-utils
[tests] Use flake8 and isort versions defined in openwisp-utils

interop-dev/django-netjsongraph,netjson/django-netjsongraph,netjson/django-netjsongraph,interop-dev/django-netjsongraph,netjson/django-netjsongraph,interop-dev/django-netjsongraph,netjson/django-netjsongraph