docs(message): remove the mention of Sticker objects

message.go

@@ -148,7 +148,7 @@ type Message struct {
 	// The thread that was started from this message, includes thread member object
 	Thread *Channel `json:"thread,omitempty"`
 
-	// An array of Sticker objects, if any were sent.
+	// An array of StickerItem objects, representing sent stickers, if there were any.
 	StickerItems []*StickerItem `json:"sticker_items"`
 }