Permit semver-compatible versions of proc-macro-crate

[adam-azarchs]

The dependency on proc-macro-crate

num_enum/num_enum_derive/Cargo.toml

Line 36 in e5dc4da

proc-macro-crate = { version = ">= 1, <= 3", optional = true }

specifies <=3, which precludes updating to the latest version, e.g. v3.3.0. I suspect that this constraint was unintentional and was meant to be <4