Nerf colors Vim uses for MatchParen and Search highlighting

This is a pretty ugly hack to work around the problem that any attempts
to influence highlight colors in Vim using the `highlight` command were
ignored by Urxvt (not by Xfce4 terminal and few others I tried).

dotfiles.config/Xlib/colorscheme/zenburn.Xdefaults

 URxvt.color3:           #dfaf8f
 URxvt.color4:           #506070
 URxvt.color5:           #dc8cc3
-URxvt.color6:           #467071
+URxvt.color6:           #356061
 URxvt.color7:           #DCDCCC
 URxvt.color8:           #808080
 URxvt.color9:           #cc9393
 URxvt.color10:          #7f9f7f
-URxvt.color11:          #906959
+URxvt.color11:          #222222
 URxvt.color12:          #94bff3
 URxvt.color13:          #ec93d3
 URxvt.color14:          #93e0e3