Add types export to package.json

[Khauri]

This PR adds the "types" field to the exports in the package.json pointed to the generated dist/index.d.ts.

Without it, my project was unable to pull any types for yieldparser, which made it a tad bit harder to work with.

This is the error typsecript reported:

Could not find a declaration file for module 'yieldparser'. 'node_modules/yieldparser/dist/yieldparser.module.js' implicitly has an 'any' type.
  There are types at 'node_modules/yieldparser/dist/index.d.ts', but this result could not be resolved when respecting package.json "exports". The 'yieldparser' library may need to update its package.json or typings.

Let me know if you find any issues.

Also thanks for creating such a cool parser generator. I've found it really nice for things that are too complex for regex but not so much that I'd want to write a whole grammar for