Change _build to something that doesn't start with underscore

[birkskyum]

I have issues with jekyll, which is used by github pages for SSG.

The issues is that it can't find files inside paths that starts with _:

https://docs.github.com/en/enterprise/2.14/user/articles/files-that-start-with-an-underscore-are-missing

How can I rename _build to something else, so my assets (.js / .css) can be found. Currently it's only the .html files that can be found.

[birkskyum]

For anyone hitting this issue, add a .nojekyll file to the root of the gh-pages branch:

• https://github.com/maplibre/maplibre-style-spec/pull/565