update debian init script

run as root firstly, then switch to $USER by "-a" parameter, so that we can bind to port lower than 1024 when running as normal user.

debian/shadowsocks-libev.init

@@ -56,9 +56,9 @@ do_start()
     #   0 if daemon has been started
     #   1 if daemon was already running
     #   2 if daemon could not be started
-    start-stop-daemon --start --quiet --pidfile $PIDFILE --chuid $USER:$GROUP --exec $DAEMON --test > /dev/null \
+    start-stop-daemon --start --quiet --pidfile $PIDFILE --chuid root:$GROUP --exec $DAEMON --test > /dev/null \
         || return 1
-    start-stop-daemon --start --quiet --pidfile $PIDFILE --chuid $USER:$GROUP --exec $DAEMON -- \
+    start-stop-daemon --start --quiet --pidfile $PIDFILE --chuid root:$GROUP --exec $DAEMON -- \
         -c "$CONFFILE" -a "$USER" -u -f $PIDFILE $DAEMON_ARGS \
         || return 2
 }