Use a newer version of protoc-gen-ts?

[NfNitLoop]

Thanks for making this for Deno!

I noticed this project was based on an older version of protoc-gen-ts. There have been some updates with nice new features since then, including fixes for TypeScript v4 (https://github.com/thesayyn/protoc-gen-ts/issues/31), proper support for possibly undefined types (https://github.com/thesayyn/protoc-gen-ts/issues/20), and support for Protobuf oneof fields (https://github.com/thesayyn/protoc-gen-ts/pull/40)

Would be nice to have those features here too!

[thesayyn]

Also, it would make sense to directly depend on protoc-gen-ts as we introduce new fixes and features.