Avoid reaching brightness 0 too easy

Apparently with some distros, raching 0 will turn off the display
completely.  Step of 49 makes it easy to avoid that while still keeping
the advantage of huge step.

dotfiles/i3/config

 bindsym $mod+Shift+c        exec "bmo uris -1 | bmo xuris -c"
 bindsym $mod+i              exec "bmo menu uris"
 bindsym $mod+Shift+i        exec "bmo menu www_hist"
-bindsym $mod+d              exec xbacklight -dec 50
+bindsym $mod+d              exec xbacklight -dec 49
 bindsym $mod+Shift+d        exec xbacklight -inc 5
 bindsym $mod+q              exec "bmo clip cat | sed 's/^/g /' | bmo uris | bmo xuris"
 bindsym $mod+Shift+q        exec "bmo clip cat | perl -ne '$a=qx(bmo menu query); chomp $a; print qq/$a $_/' | bmo uris | bmo xuris"