Update criterion requirement from 0.5 to 0.6

Updates the requirements on [criterion](https://github.com/bheisler/criterion.rs) to permit the latest version.
- [Changelog](https://github.com/bheisler/criterion.rs/blob/master/CHANGELOG.md)
- [Commits](bheisler/criterion.rs@0.5.0...0.6.0)

---
updated-dependencies:
- dependency-name: criterion
  dependency-version: 0.6.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

postgres/Cargo.toml

@@ -48,4 +48,4 @@ tokio-postgres = { version = "0.7.13", path = "../tokio-postgres" }
 tokio = { version = "1.0", features = ["rt", "time"] }
 
 [dev-dependencies]
-criterion = "0.5"
+criterion = "0.6"

tokio-postgres/Cargo.toml

@@ -70,7 +70,7 @@ socket2 = { version = "0.5", features = ["all"] }
 
 [dev-dependencies]
 futures-executor = "0.3"
-criterion = "0.5"
+criterion = "0.6"
 env_logger = "0.11"
 tokio = { version = "1.0", features = [
     "macros",