remove flake8 upper bound

setup.py

@@ -26,7 +26,7 @@ def read(*filenames, **kwargs):
     maintainer='Thomas Grainger',
     maintainer_email='[email protected]',
     version='2.0.1.dev0',
-    install_requires=['flake8>=2, <5.0.0'],
+    install_requires=['flake8>=2'],
     url='https://github.com/PyCQA/flake8-commas/',
     long_description=readme + '\n\n' + history,
     description='Flake8 lint for trailing commas.',