Set cursor size

See also https://unix.stackexchange.com/questions/423633/huge-mouse-cursor-in-some-windows

Thanks to oftc#i3 for help.

dotfiles/config/Xlib/global.Xdefaults

@@ -1,3 +1,5 @@
+Xcursor.size:               8
+
 URxvt.mapAlert:             true
 
 !## extensions