Switch to Default HTTP client for Prometheus queries

A new / empty client isn't necessary for these queries.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

gateway/main.go

@@ -167,7 +167,7 @@ func main() {
 		)
 	}
 
-	prometheusQuery := metrics.NewPrometheusQuery(config.PrometheusHost, config.PrometheusPort, &http.Client{}, version.BuildVersion())
+	prometheusQuery := metrics.NewPrometheusQuery(config.PrometheusHost, config.PrometheusPort, http.DefaultClient, version.BuildVersion())
 	faasHandlers.ListFunctions = metrics.AddMetricsHandler(faasHandlers.ListFunctions, prometheusQuery)
 	faasHandlers.ScaleFunction = scaling.MakeHorizontalScalingHandler(handlers.MakeForwardingProxyHandler(reverseProxy, forwardingNotifiers, urlResolver, nilURLTransformer, serviceAuthInjector))