Update bindgen requirement from 0.50.0 to 0.51.0 (#222)

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/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/rust-bindgen/compare/v0.50.0...v0.51.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

wasmtime-runtime/Cargo.toml

@@ -30,7 +30,7 @@ winapi = { version = "0.3.6", features = ["winbase", "memoryapi"] }
 
 [build-dependencies]
 cmake = "0.1.35"
-bindgen = "0.50.0"
+bindgen = "0.51.0"
 regex = "1.0.6"
 
 [features]

wasmtime-wasi-c/Cargo.toml

@@ -22,7 +22,7 @@ libc = "0.2.50"
 
 [build-dependencies]
 cmake = "0.1.35"
-bindgen = "0.50.0"
+bindgen = "0.51.0"
 
 [badges]
 maintenance = { status = "experimental" }