incompatible engine due to Nodejs caret version

[Tarnadas]

Hey,

the caret versioning of the engine field in package.json forces me to use Nodejs v20.
https://github.com/defuse-protocol/defuse-sdk/blob/beta/package.json#L134-L136
When I use a newer Nodejs version it fails to install.

You can just define a minimum Nodejs version instead