Update to dwm 6.0
>From Bug Hunting in PR pkg/45737

Changes in the 6.0:

- several Xinerama fixes;
- a new approach to hide clients into negative space rather than positive;
- the return of the nmaster functionality (Mod1-i, Mod1-d);
- better EWHM support for floating windows;
- fixed sloppy focussing of empty screens;
- a new default color scheme (actually a new old one, now bluedark rather than
  bluegray).

(asau)