Update num requirement from 0.2 to 0.4

Updates the requirements on [num](https://github.com/rust-num/num) to permit the latest version.
- [Release notes](https://github.com/rust-num/num/releases)
- [Changelog](https://github.com/rust-num/num/blob/master/RELEASES.md)
- [Commits](rust-num/num@num-0.2.0...num-0.4.0)

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

lib/Cargo.toml

@@ -10,7 +10,7 @@ readme = "README.md"
 repository = "https://github.com/hacspec/hacspec"
 
 [dependencies]
-num = "0.2"
+num = "0.4"
 secret_integers = { path = "../utils/secret-integers", version = "0.1.7" } #FIXME: publish new version
 abstract_integers = { path = "../utils/abstract-integers", version = "0.1.5" } #FIXME: publish new version
 hacspec-attributes = { path = "../utils/attributes",  optional = true, version = "0.1.0-beta.1" }

utils/abstract-integers/Cargo.toml

@@ -10,4 +10,4 @@ license = "Apache-2.0"
 readme = "README.md"
 
 [dependencies]
-num = "0.2"
+num = "0.4"

utils/dev/Cargo.toml

@@ -10,6 +10,6 @@ repository = "https://github.com/hacspec/hacspec"
 hacspec-lib = { path = "../../lib", version = "0.1.0-beta.1" }
 
 rand = "0.7"
-num = "0.2"
+num = "0.4"
 serde_json = "1.0"
 serde = {version = "1.0", features = ["derive"]}