Fix Next.js SSR Docs (#2638)
Without this change, Next.js latest fails to compile and complains with:
```
./node_modules/@react-spectrum/table/dist/main.css
Global CSS cannot be imported from within node_modules.
Read more: https://nextjs.org/docs/messages/css-npm
Location: node_modules/@react-spectrum/table/dist/module.js
```
NB: In the future, it might be nice to template this section in the doc
to automatically include the requisite imports, but I'm not familiar
enough with this project, nor Next, nor MDX to make that change at the
moment.
