TR-4678 Update sample NGINX configuration file in guide on setting up…

… deep links

content/docs/tech-resources/deep-links-self-serve.md

@@ -488,6 +488,8 @@ To check your files are served correctly and Android auto-verify is working - se
 1. Add `location` blocks to your config to declare the spec files on your tracking domain, which will allow Android to [auto-verify](#android-testing-auto-verify). Here is a complete example, including the engagement-tracking `proxy-pass` block done in step 1.
 
     ```
+    resolver 10.0.0.2 valid=10s;
+
     server {
         listen 80;
         listen 443 ssl http2;
@@ -513,7 +515,9 @@ To check your files are served correctly and Android auto-verify is working - se
 
         # pass all other requests through to SparkPost engagement tracking
         location / {
-            proxy_pass      https://spgo.io;
+            set $backend "spgo.io";
+            proxy_pass      https://$backend;
+            proxy_set_header Host $host;
             proxy_set_header X-Forwarded-For $remote_addr; # pass the client IP to the open & click tracker
             server_tokens off; # suppress NGINX giving version/OS information on error pages
         }