Missing lockfile

Hi there! I'm currently trying to package the Fyrox project manager for Nix (NixOS/nixpkgs#503737) and one issue I've been hitting is the lack of a Cargo.lock file for reproducible building of the project.

Normally Rust crate repositories will not add Cargo.lock to .gitignore, as to ensure that they are built with specific crate versions across machines. This would also be beneficial for debugging problems from users building from source, as their dependencies should match the versions committed to the repo.