sh compatibility in minor scripts

.scripts/lockscreen

@@ -1,19 +1,19 @@
-#!/bin/bash
+#!/bin/sh
 
 rm -f /tmp/locked.png
 
 # If `imagemagick` is not installed, use a blank screen.
-[[ -f /usr/bin/convert ]] &&
+[ -f /usr/bin/convert ] &&
 scrot -m -z /tmp/base.png &&
 pgrep -x dunst && notify-send -i ~/.scripts/lock.png "Locking computer..." &&
 convert /tmp/base.png -blur 0x8 /tmp/locked.png
 
 # Pause music (mocp, mpd and send the pause key to all mpv videos):
-mocp -P &>/dev/null
-mpc pause &>/dev/null
-pauseallmpv &>/dev/null
+mocp -P >/dev/null 2>&1
+mpc pause >/dev/null 2>&1
+pauseallmpv >/dev/null 2>&1
 
 i3lock -e -f -c 000000 -i /tmp/locked.png
 
 # In five seconds, turn off display unless key press in last 4 seconds.
-sleep 5 && [[ 4000 -lt $(xssstate -i) ]] &&  pgrep -x i3lock && xset dpms force off
+sleep 5 && [ 4000 -lt "$(xssstate -i)" ] &&  pgrep -x i3lock && xset dpms force off