This manually downloads the old AppImage runtime (now marked as obsolete), to prevent appimage-builder v1.1.0 from failing to make the AppImage. The download URL appimage-builder v1.1.0 uses for the AppImage runtime is hardcoded into the tool, and unfortunately it's been recently removed, so this is merely a workaround, until hopefully a future appimage-builder release fixes this. See: https://redirect.github.com/AppImageCrafters/appimage-builder/issues/375