Add thumbnail to Audio (#240)

media.go

@@ -80,6 +80,7 @@ type Audio struct {
 
 	// (Optional)
 	Caption   string `json:"caption,omitempty"`
+	Thumbnail *Photo `json:"thumb,omitempty"`
 	Title     string `json:"title,omitempty"`
 	Performer string `json:"performer,omitempty"`
 	MIME      string `json:"mime_type,omitempty"`

sendable.go

@@ -59,7 +59,7 @@ func (a *Audio) Send(b *Bot, to Recipient, opt *SendOptions) (*Message, error) {
 
 	embedSendOptions(params, opt)
 
-	msg, err := b.sendObject(&a.File, "audio", params, nil)
+	msg, err := b.sendObject(&a.File, "audio", params, thumbnailToFilemap(a.Thumbnail))
 	if err != nil {
 		return nil, err
 	}