fix: use Quad9 (9.9.9.9) DNS resolver per Plausible recommendation

Author: mroderick

config/nginx.conf.erb

@@ -10,7 +10,7 @@ http {
   server_tokens off;
 
   # DNS resolver for proxy_pass
-  resolver 8.8.8.8 1.1.1.1 valid=30s;
+  resolver 9.9.9.9 valid=30s;
 
   # Security headers
   add_header X-Frame-Options "SAMEORIGIN" always;