Use $(fn)

This is the recommended way in jQuery 3.x.

Signed-off-by: XhmikosR <xhmikosr@gmail.com>

scripts/pi-hole/js/customdns.js

@@ -37,7 +37,7 @@ function showAlert(type, message) {
   alertElement.delay(8000).fadeOut(2000);
 }
 
-$(document).ready(function () {
+$(function () {
   $("#btnAdd").on("click", addCustomDNS);
 
   table = $("#customDNSTable").DataTable({