Include types in package.json

[duncanmak]

I'm using the router from skypack.dev and it recommends packages to include typescript dts files in the types field in package.json.

https://docs.skypack.dev/package-authors/package-checks#types

I have made a simple commit to add that: https://github.com/duncanmak/router/commit/5d5636459a80c5ee5e141d11cb6e9dfaecd2f6c4

Please let me know if I should make a PR.