Fix typings

[nbaum]

Fixes, for me, the TypeScript error:

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

May fix #50 generally, but I don't understand TypeScript well enough to be sure this this is a sufficient fix in all situations.