build(deps): update itertools requirement from 0.12 to 0.13 (#921)

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@v0.12.0...v0.13.0)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

generator/Cargo.toml

@@ -11,7 +11,7 @@ publish = false
 # file is generated as currently checked in): 
 bindgen = "=0.69.4"
 heck = "0.5"
-itertools = "0.12"
+itertools = "0.13"
 nom = "7.1"
 once_cell = "1.7"
 proc-macro2 = "1.0"