add pep8-naming to pep8 tests
diff --git a/tox.ini b/tox.ini
index 4248db3..27b652a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -41,4 +41,4 @@
 
 [flake8]
 exclude = .tox,*.egg
-select = E,W,F
+select = E,W,F,N