Add refund transaction API

Author: AchoArnold

client.go

@@ -6,7 +6,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 )
 
@@ -102,7 +101,7 @@ func (client *Client) do(req *http.Request) (*Response, error) {
 		return resp, err
 	}
 
-	_, err = io.Copy(ioutil.Discard, httpResponse.Body)
+	_, err = io.Copy(io.Discard, httpResponse.Body)
 	if err != nil {
 		return resp, err
 	}
@@ -119,7 +118,7 @@ func (client *Client) newResponse(httpResponse *http.Response) (*Response, error
 	resp := new(Response)
 	resp.HTTPResponse = httpResponse
 
-	buf, err := ioutil.ReadAll(resp.HTTPResponse.Body)
+	buf, err := io.ReadAll(resp.HTTPResponse.Body)
 	if err != nil {
 		return nil, err
 	}