lock: sleep a bit to let i3lock lock the screen

We could let i3lock fork to notify us but then, we have to spy on it to
know when the screen is unlocked.

bin/xss-lock

@@ -26,6 +26,7 @@ case "$1" in
         if [ -e /proc/self/fd/${XSS_SLEEP_LOCK_FD:--1} ]; then
             trap 'kill %%' TERM INT
             i3lock -n $i3lock_options {XSS_SLEEP_LOCK_FD}<&- &
+            sleep 0.3           # Slight race condition, better than an active loop
             exec {XSS_SLEEP_LOCK_FD}<&-
             wait
         else