added create date calculator for channel.

http.go

@@ -2,6 +2,7 @@ package revoltgo
 
 import (
 	"bytes"
+	"fmt"
 	"io/ioutil"
 	"net/http"
 )
@@ -26,6 +27,10 @@ func (c Client) Request(method, path string, data []byte) ([]byte, error) {
 		return []byte{}, err
 	}
 
+	if !(resp.StatusCode >= 200 && resp.StatusCode < 300) {
+		return []byte{}, fmt.Errorf(resp.Status)
+	}
+
 	defer resp.Body.Close()
 	body, err := ioutil.ReadAll(resp.Body)