Update black to fix following error

ImportError: /home/runner/.cache/pre-commit/repob3mj_5qk/py_env-python3/lib/python3.9/site-packages/typed_ast/_ast3.cpython-39-x86_64-linux-gnu.so: undefined symbol: _PyUnicode_DecodeUnicodeEscape
The original issue is python/typed_ast#169

.pre-commit-config.yaml

@@ -55,7 +55,7 @@ repos:
           - --remove-duplicate-keys
           - --remove-unused-variables
   - repo: https://github.com/psf/black
-    rev: 20.8b1
+    rev: 21.10b0
     hooks:
       - id: black
   - repo: https://github.com/pre-commit/mirrors-prettier