Update pre-commit hooks

.pre-commit-config.yaml

 repos:
-  - repo: https://github.com/ambv/black
+  - repo: https://github.com/psf/black
     rev: 19.10b0
     hooks:
       - id: black
-  - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v2.4.0
+  - repo: https://gitlab.com/pycqa/flake8
+    rev: 3.8.2
     hooks:
       - id: flake8