Update parking_lot requirement from 0.11 to 0.12

Updates the requirements on [parking_lot](https://github.com/Amanieu/parking_lot) to permit the latest version.
- [Release notes](https://github.com/Amanieu/parking_lot/releases)
- [Changelog](https://github.com/Amanieu/parking_lot/blob/master/CHANGELOG.md)
- [Commits](Amanieu/parking_lot@0.11.0...0.12.0)

---
updated-dependencies:
- dependency-name: parking_lot
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

bb8/Cargo.toml

@@ -12,7 +12,7 @@ readme = "../README.md"
 async-trait = "0.1"
 futures-channel = "0.3.2"
 futures-util = { version = "0.3.2", default-features = false, features = ["channel"] }
-parking_lot = "0.11"
+parking_lot = "0.12"
 tokio = { version = "1.0", features = ["rt", "time", "parking_lot"] }
 
 [dev-dependencies]