Added type to export

[TessavWalstijn]

Moving from Webpack 4 to Vite 4.

When we build our application we get the error that Vite:

✘ [ERROR] Could not resolve "./data-model"

    node_modules/@rdfjs/types/index.d.ts:3:14:
      3 │ export * from './data-model';
        ╵               ~~~~~~~~~~~~~~

✘ [ERROR] Could not resolve "./stream"

    node_modules/@rdfjs/types/index.d.ts:4:14:
      4 │ export * from './stream';
        ╵               ~~~~~~~~~~

✘ [ERROR] Could not resolve "./dataset"

    node_modules/@rdfjs/types/index.d.ts:5:14:
      5 │ export * from './dataset';
        ╵               ~~~~~~~~~~~

✘ [ERROR] Could not resolve "./query"

    node_modules/@rdfjs/types/index.d.ts:6:14:
      6 │ export * from './query';
        ╵               ~~~~~~~~~

I was able to solve the issue locally by editing the index.d.ts from this package.

I hope with this change to make rdfjs accessible for Vite users as well.