Add trailing slash to version selector URL's

[wbekerom]

URL's in version selector need a trailing slash in order to be in line with other links in generated docs. This ensures that the relative paths to js / css always work. For me the URL's did not work when deploying to Azure blob storage, hosted as "static website".

This probably needs to be fixed in templates/redirect.html and version-select.js in both themes.
I can send you a PR for this if you like.

Similar to: squidfunk/mkdocs-material#2434

[jimporter]

Fixed in 79827d4 and 05eb98c

[wbekerom]

Thanks!