Add rng parameter in encapsulate method of a Kem trait

[ChickenLover]

Hello, I am trying to realize Round5 KEM in Rust and implement your Kem trait for it. The problem is Round5 requires that both generate and encapsulate methods take a source of random as a parameter. It would be great if you'll add rng: &mut dyn Random parameter in types::Kem::encapsulate method