html: Avoid old tidy on macOS
html: Avoid old tidy on macOS

On macOS, Apple's command line toolchain installs very old `tidy`
command (It was released on 31 Oct 2006). It does not consider new specs
such as HTML5 so we should avoid it.

IngoHeimbach/ale,w0rp/ale,IngoHeimbach/ale,IngoHeimbach/ale,adriaanzon/ale,neersighted/ale,hernot/ale,hernot/ale,neersighted/ale,neersighted/ale,w0rp/ale,hernot/ale,w0rp/ale