build(deps): update num-bigint requirement from 0.3.1 to 0.4.0 (#532)

Updates the requirements on [num-bigint](https://github.com/rust-num/num-bigint) to permit the latest version.
- [Release notes](https://github.com/rust-num/num-bigint/releases)
- [Changelog](https://github.com/rust-num/num-bigint/blob/master/RELEASES.md)
- [Commits](rust-num/num-bigint@num-bigint-0.3.1...num-bigint-0.4.0)

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

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

uint/Cargo.toml

@@ -32,7 +32,7 @@ required-features = ["std"]
 
 [dev-dependencies]
 criterion = "0.3.0"
-num-bigint = "0.3.1"
+num-bigint = "0.4.0"
 
 [target.'cfg(all(unix, target_arch = "x86_64"))'.dev-dependencies]
 rug = { version = "1.6.0", default-features = false, features = ["integer"] }