[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

setup.cfg

@@ -10,7 +10,7 @@ author_email = kilian.lieret@posteo.de
 maintainer = Kilian Lieret
 maintainer_email = kilian.lieret@posteo.de
 license = MIT
-license_file = LICENSE.txt
+license_files = LICENSE.txt
 classifiers =
     License :: OSI Approved :: MIT License
     Operating System :: OS Independent