Update criterion requirement from 0.3 to 0.4

Updates the requirements on [criterion](https://github.com/bheisler/criterion.rs) to permit the latest version.
- [Release notes](https://github.com/bheisler/criterion.rs/releases)
- [Changelog](https://github.com/bheisler/criterion.rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/bheisler/criterion.rs/compare/0.3.0...0.4.0)

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

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

postgres/Cargo.toml

@@ -45,5 +45,5 @@ tokio = { version = "1.0", features = ["rt", "time"] }
 log = "0.4"
 
 [dev-dependencies]
-criterion = "0.3"
+criterion = "0.4"
 tokio = { version = "1.0", features = ["rt-multi-thread"] }

tokio-postgres/Cargo.toml

@@ -61,7 +61,7 @@ tokio-util = { version = "0.7", features = ["codec"] }
 
 [dev-dependencies]
 futures-executor = "0.3"
-criterion = "0.3"
+criterion = "0.4"
 env_logger = "0.9"
 tokio = { version = "1.0", features = [
     "macros",