storage-ng/public-address-proxy: fixed typo

hosts/storage-ng/public-access-proxy/proxy.nix

@@ -77,7 +77,7 @@ in {
       enable = true;
       config = ''
         resolvers dns
-          nameservers quad9 9.9.9.9:53
+          nameserver quad9 9.9.9.9:53
           hold valid 1s
 
         frontend http-in