deno.land/x can't resolve jsxImportSource

In [nano_jsx](https://github.com/nanojsx/nano-jsx-deno-example/blob/master/deno.json) I would like to import the `jsx-runtime` like so:

```json
{
"compilerOptions": {
"jsx": "react-jsx",
"jsxImportSource": "https://deno.land/x/nano_jsx"
}
}
```

But on `deno run`, this failes to resolve `error: Module not found "https://deno.land/x/nano_jsx/jsx-runtime"`. Even though there is an `index.ts` file inside that directory and it contains the jsx-runtime.

---

It would be nice if deno.land/x would be able to resolve index.js and index.ts files from inside a jsx-runtime directory.