docs: update ref documentation

The innerRef prop was updated to ref. I've changed this in the documentation.

Fixes # (issue)

Check the documentation in the docs folder.

[ ] My code follows the style guidelines of this project (I have run pnpm run lint)
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[ ] New and existing unit tests pass locally with my changes (I have run pnpm run test:ci-with-server/pnpm run test)
[ ] I have performed a self-review of my own code
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FormidableLabs / nuka-carousel