Update bindgen requirement from 0.66.1 to 0.68.1 (#45)

Updates the requirements on [bindgen](https://github.com/rust-lang/rust-bindgen) to permit the latest version.
- [Release notes](https://github.com/rust-lang/rust-bindgen/releases)
- [Changelog](https://github.com/rust-lang/rust-bindgen/blob/main/CHANGELOG.md)
- [Commits](rust-lang/rust-bindgen@v0.66.1...v0.68.1)

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

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

rlottie-sys/Cargo.toml

@@ -16,5 +16,5 @@ rust-version = "1.56"
 links = "rlottie"
 
 [build-dependencies]
-bindgen = { version = "0.66.1", features = ["prettyplease", "runtime"], default-features = false }
+bindgen = { version = "0.68.1", features = ["prettyplease", "runtime"], default-features = false }
 pkg-config = "0.3.22"