fix: [skeleton] Fix the skeleton MANIFEST.in
Since version 0.42 of check-manist, prune is intended for folder and exclude for file See https://github.com/mgedmin/check-manifest/issues/115#issuecomment-625096256
Since version 0.42 of check-manist, prune is intended for folder and exclude for file See https://github.com/mgedmin/check-manifest/issues/115#issuecomment-625096256