Jazzy docs: assets folder is missing in gh-pages

[0bmxa]

New Issue Checklist

• [x] ~Updated SwiftLint to the latest version~ N/A
• [x] I searched for existing GitHub issues

Describe the bug

The assets folder, used by the Jazzy docs, is missing in the published gh-pages. It seems to be only used by the index.html, and is expected to be found diretly at /assets, but it's not.

• Expected e.g. here: https://github.com/realm/SwiftLint/blob/61619db0957ee9171273145e4d65b53dd57a3432/index.html#L329
• 404 here: https://realm.github.io/SwiftLint/assets/screenshot.png
• Screenshot not visible here (should be right below the badges): https://realm.github.io/SwiftLint/index.html

Complete output when running SwiftLint, including the stack trace and command used

N/A

Environment

N/A