flake8 fix

setup.cfg

diff --git a/setup.cfg b/setup.cfg
index 369788b..9bbbd03 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -7,4 +7,4 @@
 exclude = .git, __pycache__, build, dist, docs, tools, venv
 ignore =
     # required for pretty matrix formatting: multiple spaces after `,` and `[`
-    E201, E241
+    E201, E241, W504