v7.3.2.0: Update AJAX request parameter in add.js

This commit changes the element ID fetched to set the 'serv' parameter in an AJAX request. The 'serv' value source has been altered from '#serv_for_vars' to '#serv_for_lets'. This update ensures that the correct data is passed when making the request.

app/static/js/add.js

@@ -933,7 +933,7 @@ $( function() {
 			$.ajax({
 				url: "/app/add/lets",
 				data: {
-					serv: $('#serv_for_vars').val(),
+					serv: $('#serv_for_lets').val(),
 					lets_domain: lets_domain,
 					lets_email: lets_email
 				},