Update num-bigint requirement from 0.3 to 0.4

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-0.3.0...num-bigint-0.4.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

Cargo.toml

@@ -26,7 +26,7 @@ ark-relations = { git = "https://github.com/arkworks-rs/snark", default-features
 
 derivative = { version = "2", features = ["use_core"] }
 tracing = { version = "0.1", default-features = false, features = [ "attributes" ] }
-num-bigint = {version = "0.3", default-features = false }
+num-bigint = {version = "0.4", default-features = false }
 num-traits = {version = "0.2", default-features = false }
 
 [dev-dependencies]