[requires.io] dependency update

Author: requires

tox.ini

@@ -125,7 +125,7 @@ skip_install = True
 
 deps =
     flake8-bugbear==21.3.2
-    flake8==3.8.4
+    flake8==3.9.0
     mccabe==0.6.1
     pep8-naming==0.11.1
     pycodestyle==2.7.0