[Bug Report/Build Failure/Feature Request] Upgrade to newer crystal version

[RTUnreal]

Describe the bug A clear and concise description of what the bug is.

The app doesn't compile on newer crystal versions.

It might even make it hard to maintain the app in the future if stuck on crystal 1.0.0.

Additional context I can't integrate mango into nixpkgs because crystal 1.0.0 is not available as a compile toolchain.

If there is a specific question that needs to be answered, you can ask me.