docs: hotfix docs dropdown: update versions.json reference in index.html

[LKasianAnsys]

Addresses #38

The VISOR docs version switcher drop-down on the https://visor.docs.pyansys.com/versions.json landing page is not currently populating. A docs configuration update was added in #106 for future doc builds (dev and release/stable).

The dev docs build ran after that PR was merged, but that only published to the versions/dev directory, and doesn't touch the main index.html or 1.0 or stable directories. The 1.0 and stable directories will be overwritten on the next patch release, and are internally consistent. But index.html will remain broken until the next release.

This adds a hotfix onto the gh-pages branch to update index.html correctly, so that we don't need to wait for the next release for the fix.