Merge pull request #1686 from praw-dev/pre-commit

Update pre-commit revision line to be an actual tag

Author: bboe

.pre-commit-config.yaml

@@ -4,4 +4,4 @@ repos:
   - id: black
     language_version: python3
   repo: https://github.com/psf/black
-  rev: stable
+  rev: 20.8b1