fix url building

lib.go

@@ -34,7 +34,7 @@ func (c *Cli) Do(method string, strurl string, body []byte) (*http.Response, err
 		if strings.HasSuffix(addr, "/") {
 			addr = addr[:len(addr)-1]
 		}
-		if !strings.HasPrefix(strurl, "") {
+		if !strings.HasPrefix(strurl, "/") {
 			strurl = "/" + strurl
 		}
 		strurl = addr + strurl