specify go1.12 way too

README.md

@@ -28,7 +28,22 @@ import (
 )
 
 // Setup an HTTP client with a custom transport
-transport := http.DefaultTransport.(*http.Transport).Clone()
+transport := &http.Transport{
+    Proxy: ProxyFromEnvironment,
+	DialContext: (&net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 30 * time.Second,
+		DualStack: true,
+	}).DialContext,
+	ForceAttemptHTTP2:     true,
+	MaxIdleConns:          100,
+	IdleConnTimeout:       90 * time.Second,
+	TLSHandshakeTimeout:   10 * time.Second,
+	ExpectContinueTimeout: 1 * time.Second,
+}
+// or, starting with go1.13 simply use:
+// transport := http.DefaultTransport.(*http.Transport).Clone()
+
 transport.TLSClientConfig = &tls.Config{RootCAs: certPool}
 client := &http.Client{Transport: transport}