Upgrade flake8 to 3.8.4 (home-assistant#41117)

https://flake8.pycqa.org/en/latest/release-notes/3.8.4.html

Author: scop

.pre-commit-config.yaml

@@ -22,7 +22,7 @@ repos:
           - --quiet-level=2
         exclude_types: [csv, json]
   - repo: https://gitlab.com/pycqa/flake8
-    rev: 3.8.3
+    rev: 3.8.4
     hooks:
       - id: flake8
         additional_dependencies:

requirements_test_pre_commit.txt

@@ -4,7 +4,7 @@ bandit==1.6.2
 black==20.8b1
 codespell==1.17.1
 flake8-docstrings==1.5.0
-flake8==3.8.3
+flake8==3.8.4
 isort==5.5.3
 pydocstyle==5.1.1
 pyupgrade==2.7.2