Update repository URL for Flake8

Committed via https://github.com/asottile/all-repos

Author: jugmac00

.pre-commit-config.yaml

@@ -8,7 +8,7 @@ repos:
     hooks:
     - id: pyupgrade
       args: [--py36-plus]
-  - repo: https://gitlab.com/pycqa/flake8
+  - repo: https://github.com/PyCQA/flake8
     rev: "3.8.4"
     hooks:
       - id: flake8