Silently fails under Linux if xwininfo/xprop is missing

Fails without further notice if xprop or xwininfo because they are either not installed, or not present in the PATH variable. If you ask me the promise should fail with a proper error when something fails (or throw an Error for the sync variant). The current behaviour makes debugging the root of the problem quite difficult.

https://github.com/sindresorhus/active-win/blob/430e6efc02823c1b04331a987012a519c360ab23/lib/linux.js#L109-L111

Also you might want to add that there is no Wayland support at the moment to the documentation especially considering the increasing popularity of Wayland.

I might PR this myself when I find the time.