Fix incorrect config filename in update script

The update script backs up the config file to `/root/config.bak`, but
then tries to restore it from `/root/config.yml.bak` (which obviously
won't be found).

This looks like a typo in the backup command, so update that command to
use the same filename as the restore command.

Signed-off-by: Ross Simpson <ross@rosssimpson.com>

scripts/update_pwnagotchi.sh

@@ -89,7 +89,7 @@ fi
 
 if [ $BACKUPCONFIG -eq 1 ]; then
     echo "[+] Creating backup of config.yml and hostname references"
-    mv /root/pwnagotchi/config.yml /root/config.bak -f
+    mv /root/pwnagotchi/config.yml /root/config.yml.bak -f
     mv /etc/hosts /root/hosts.bak -f
     mv /etc/hostname /root/hostname.bak -f
     mv /etc/motd /etc/motd.bak -f