ops: Set expires -1 header on 2s server cached responses

production/nginx/location-api.conf

@@ -140,7 +140,8 @@ location @mempool-api-v1-cache-normal {
 	proxy_cache_valid 200 2s;
 	proxy_redirect off;
 
-	expires 2s;
+	# cache for 2 seconds on server, but send expires -1 so browser doesn't cache
+	expires -1;
 }
 
 location @mempool-api-v1-cache-disabled {