Ignore Flake8 rule W503

As defined in https://www.flake8rules.com/rules/W503.html, this rule
goes against the PEP8 recommendation and conflicts with W504.

In the code, the rule results in a false-positive in
patterns/behavioral/specification.py.

Author: imankulov

setup.cfg

@@ -1,6 +1,6 @@
 [flake8]
 max-line-length = 120
-ignore = E266 E731
+ignore = E266 E731 W503
 exclude = .venv*
 
 [tool:pytest]