Update hashbrown requirement from 0.5.0 to 0.6.0 (#274)

Updates the requirements on [hashbrown](https://github.com/rust-lang/hashbrown) to permit the latest version.
- [Release notes](https://github.com/rust-lang/hashbrown/releases)
- [Changelog](https://github.com/rust-lang/hashbrown/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/hashbrown/compare/v0.5.0...v0.6.0)

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

wasmtime-jit/Cargo.toml

@@ -23,7 +23,7 @@ region = "2.0.0"
 failure = { version = "0.1.3", default-features = false }
 failure_derive = { version = "0.1.3", default-features = false }
 target-lexicon = { version = "0.4.0", default-features = false }
-hashbrown = { version = "0.5.0", optional = true }
+hashbrown = { version = "0.6.0", optional = true }
 wasmparser = "0.35.1"
 
 [features]