Add a tox env to force format

Author: ralphbean

tox.ini

@@ -36,3 +36,8 @@ order_by_type = false
 skip_install = true
 deps = isort
 commands = isort --check --diff {posargs:.}
+
+[testenv:isort-format]
+skip_install = true
+deps = isort
+commands = isort {posargs:.}