Fix usage of py-test

Index: setup.cfg
--- setup.cfg.orig
+++ setup.cfg
@@ -8,7 +8,7 @@ release = register clean --all sdist bdist_wheel
 max-line-length = 140
 exclude = tests/*,*/migrations/*,*/south_migrations/*
 
-[pytest]
+[tools:pytest]
 norecursedirs = 
 	.git
 	.tox