readme update

README.md

@@ -68,8 +68,8 @@ tkt, err := cl.GetServiceTicket("HTTP/host.test.gokrb5")
 Create the HTTP request object and then call the client's SetSPNEGOHeader method passing the Service Principal Name (SPN)
 ```go
 r, _ := http.NewRequest("GET", "http://host.test.gokrb5/index.html", nil)
-cl.SetSPNEGOHeader(r)
-HTTPResp, err := http.DefaultClient.Do(r, "")
+cl.SetSPNEGOHeader(r, "")
+HTTPResp, err := http.DefaultClient.Do(r)
 ```
 
 ### Kerberos Web Service