Fix type issues

[oyvinmar]

1. Removed types from package.json (it pointed to the wrong declaration file). Typescript should find index.d.ts automatically.
2. AuthProvider need to return a JSX.Element (see [Question] JSX.Element vs React.ReactNode once again typescript-cheatsheets/react#129). It may be better to just type the props and let the rest be inferred.

[Swizec]

Thanks @oyvinmar! Great fix, I'm still pretty new to types in libraries :)

[Swizec]

@all-contributors add @oyvinmar for code

[allcontributors]

@Swizec

I've put up a pull request to add @oyvinmar! 🎉