External `themes.json` broken

[cmahnke]

Describe the bug
In layouts/partials/style.html the file https://raw.githubusercontent.com/Gogh-Co/Gogh/master/data/themes.json is included, this has changed

This breaks the build:

Error: error building site: render: failed to render pages: render of "page" failed: "/home/runner/work/xn--h-zfa.xyz/xn--h-zfa.xyz/themes/hugo-theme-shell/layouts/_default/baseof.html:3:8": execute of template failed: template: _default/single.html:3:8: executing "_default/single.html" at <partial "head.html" .>: error calling partial: "/home/runner/work/xn--h-zfa.xyz/xn--h-zfa.xyz/layouts/partials/head.html:6:7": execute of template failed: template: partials/head.html:6:7: executing "partials/head.html" at <partial "partials/style.html" .>: error calling partial: "/home/runner/work/xn--h-zfa.xyz/xn--h-zfa.xyz/themes/hugo-theme-shell/layouts/partials/style.html:32:25": execute of template failed: template: partials/style.html:32:25: executing "partials/style.html" at <$themeData.themes>: can't evaluate field themes in type []interface {}

One can replace the URL by https://raw.githubusercontent.com/Gogh-Co/Gogh/1bcd4e13564ab72108389ffe70e90845a45c31f7/data/themes.json.

Expected behavior
Don't rely on contents of external repositories without specifying the version.

Currently this theme isn't useable!