nginx: Avoid connection issues caused by IPv6 resolution

If localhost is specified in the proxyPass url, nginx will happily
resolve IPv6 addresses, even if the upstream doesn't support them.

This can result in connection issues, especially with containers that
don't support IPv6.

configuration/default.nix

@@ -60,7 +60,7 @@
         {
           forceSSL = true;
           enableACME = true;
-          locations."/" = { proxyPass = "http://localhost:${toString port}"; };
+          locations."/" = { proxyPass = "http://127.0.0.1:${toString port}"; };
         } // extra;
     in {
       "tlater.net" = host 3002 { serverAliases = [ "www.tlater.net" ]; };