upgrade to isort5 (#4399)

* Imports are no longer moved to top.
* `seed-isort-config` is no longer needed.
* Has a `black`-compatible profile/config.
* Also `isorts` the imports anywhere in the code
  (not just at the top).

Also bumps `restyled-isort` to newest version

.pre-commit-config.yaml

@@ -4,15 +4,11 @@ repos:
         language_version: python3
     repo: https://github.com/ambv/black
     rev: 19.10b0
-  - repo: https://github.com/asottile/seed-isort-config
-    rev: v2.1.1
-    hooks:
-      - id: seed-isort-config
   - hooks:
       - id: isort
         language_version: python3
     repo: https://github.com/timothycrosley/isort
-    rev: 4.3.21
+    rev: 5.4.2
   - hooks:
       - id: flake8
         language_version: python3