[pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/pre-commit/mirrors-mypy: v0.930 → v0.931](pre-commit/mirrors-mypy@v0.930...v0.931)

Author: pre-commit-ci[bot]

.pre-commit-config.yaml

@@ -28,7 +28,7 @@ repos:
     -   id: pyupgrade
         args: [--py37-plus]
   - repo: https://github.com/pre-commit/mirrors-mypy
-    rev: "v0.930"
+    rev: "v0.931"
     hooks:
       - id: mypy
         files: vdirsyncer/.*