Update itertools requirement from 0.13 to 0.14

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@v0.13.0...v0.14.0)

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

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

Author: dependabot[bot]

tests/integration/Cargo.toml

@@ -10,7 +10,7 @@ chrono = { version = "0.4", default-features = false }
 derive_more = { version = "1.0", features = ["from"] }
 fnv = "1.0"
 futures = "0.3"
-itertools = "0.13"
+itertools = "0.14"
 juniper = { path = "../../juniper", features = ["chrono"] }
 juniper_subscriptions = { path = "../../juniper_subscriptions" }
 serde = { version = "1.0", features = ["derive"] }