[1.11.x] Ignored flake8 W504 warnings.

W504 is mutually exclusive with W503 that we follow.

Backport of 58d1e9aa from master.

setup.cfg

@@ -4,7 +4,7 @@ install-script = scripts/rpm-install.sh
 
 [flake8]
 exclude = build,.git,.tox,./django/utils/lru_cache.py,./django/utils/six.py,./django/conf/app_template/*,./django/dispatch/weakref_backports.py,./tests/.env,./xmlrunner,tests/view_tests/tests/py3_test_debug.py,tests/template_tests/annotated_tag_function.py
-ignore = W601
+ignore = W504,W601
 max-line-length = 119
 
 [isort]