Update itertools requirement from 0.11 to 0.12

Updates the requirements on [itertools](https://github.com/rust-itertools/itertools) to permit the latest version.
- [Changelog](https://github.com/rust-itertools/itertools/blob/master/CHANGELOG.md)
- [Commits](rust-itertools/itertools@v0.11.0...v0.12.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Cargo.toml

@@ -33,7 +33,7 @@ url = "2.3"
 [dev-dependencies]
 backoff = { version = "0.4", features = ["futures", "tokio"] }
 http = "0.2"
-itertools = "0.11"
+itertools = "0.12"
 mockito = "1.0"
 native-tls = "0.2"
 openssl = "0.10"