build(deps): update itertools requirement from 0.10 to 0.12 (#824)

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](https://github.com/rust-itertools/itertools/compare/v0.10.0...v0.12.0)

---
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

@@ -8,7 +8,7 @@ publish = false
 [dependencies]
 bindgen = "0.64"
 heck = "0.4"
-itertools = "0.10"
+itertools = "0.12"
 nom = "7.1"
 once_cell = "1.7"
 proc-macro2 = "1.0"