fix: add extend-ignore = E203 (#324)

* fix: add extend-ignore = E203

This is needed as we are now using black code style which may raise E203.

* fix: grammar

Author: Gonzom

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-skipsdist=True
+skipsdist = True
 envlist = cov, flake8
 
 [testenv]
@@ -24,16 +24,20 @@ commands =
     flake8 tests
 
 
-# pytest Configuration
+# Pytest configuration
 [pytest]
 junit_family = xunit2
 testpaths = tests
 filterwarnings =
     ignore:.*'collections'.*'collections.abc'.*:DeprecationWarning
     ignore:Task.all_tasks() is deprecated, use asyncio.all_tasks().*:PendingDeprecationWarning
 
-# Flake8 Configuration
+
+# Flake8 configuration
 [flake8]
 # gettext() adds _() to the global namespace. This lets flake recognize it.
 builtins =
     _,
+
+# https://github.com/psf/black/blob/master/docs/the_black_code_style.md#slices
+extend-ignore = E203