Bump flake8 from 3.8.4 to 3.9.0 (#796)

dependabot-preview[bot] · web-flow · commit 65ca604971a9 · 2021-03-15T05:56:44.000Z
diff --git a/requirements.txt b/requirements.txt
@@ -1,6 +1,6 @@
 coverage==5.5
 docker==4.4.4
-flake8==3.8.4
+flake8==3.9.0
 isort==5.7.0
 -e .[sa]
 sphinx==3.5.2
