[pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/psf/black: 21.5b2 → 21.6b0](https://github.com/psf/black/compare/21.5b2...21.6b0)
- [github.com/asottile/pyupgrade: v2.19.1 → v2.19.4](https://github.com/asottile/pyupgrade/compare/v2.19.1...v2.19.4)

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
 -   repo: https://github.com/psf/black
-    rev: 21.5b2
+    rev: 21.6b0
     hooks:
     -   id: black
         args: [--safe, --quiet, --target-version, py35]
@@ -17,7 +17,7 @@ repos:
     hooks:
     -   id: flake8
 -   repo: https://github.com/asottile/pyupgrade
-    rev: v2.19.1
+    rev: v2.19.4
     hooks:
     -   id: pyupgrade
         args: [--py3-plus]