fix typo preinstall script

scripts/dappnode_install_pre.sh

@@ -148,7 +148,7 @@ install_lsof() {
 install_iptables () {
     apt-get update -y
     apt-get install iptables -y | tee -a $LOG_FILE
-    if  lsof -v >/dev/null 2>&1 ; then
+    if  iptables -v >/dev/null 2>&1 ; then
         echo -e "\e[32m \n\n Verified iptables installation \n\n \e[0m" 2>&1 | tee -a $LOG_FILE
     else
         echo -e "\e[31m \n\n WARNING: iptables not installed, Docker may not work! \n\n \e[0m" 2>&1 | tee -a $LOG_FILE