fix: use var.domain in terraform for domain verification (#223)

Author: j4y

terraform/website/dns.tf

@@ -1,7 +1,7 @@
 # domain verification with Microsoft
 resource "aws_route53_record" "mx_verification" {
   zone_id = data.aws_route53_zone.main.zone_id
-  name    = "@"
+  name    = var.domain
   type    = "MX"
   ttl     = 3600
   records = ["10 ms21173179.msv1.invalid"]
@@ -10,7 +10,7 @@ resource "aws_route53_record" "mx_verification" {
 # domain verification with Microsoft
 resource "aws_route53_record" "txt_record" {
   zone_id = data.aws_route53_zone.main.zone_id
-  name    = "@"
+  name    = var.domain
   type    = "TXT"
   ttl     = 3600
   records = ["MS=ms21173179"]