upgrade flake8 to 3.8.4 (pandas-dev#36882)

Author: Tazminia

.pre-commit-config.yaml

@@ -4,7 +4,7 @@ repos:
     hooks:
     -   id: black
 -   repo: https://gitlab.com/pycqa/flake8
-    rev: 3.8.3
+    rev: 3.8.4
     hooks:
     -   id: flake8
         additional_dependencies: [flake8-comprehensions>=3.1.0]