Fix incompatibility between flake8 and black

Author: gonzalocasas

setup.cfg

@@ -3,5 +3,8 @@ universal = 1
 
 [flake8]
 max-line-length = 120
-exclude = */migrations/*
+extend-ignore =
+    # See https://github.com/PyCQA/pycodestyle/issues/373
+    E203,
+