Temporarily fix MediaGroup test (Imgur -> GitHub)

Telegram decided that it's no longer friends with Imgur, so we will need to use the direct GitHub asset links for now. Probably will want to eventually swap this over to uploading the file since we don't want to accidentally DDOS GitHub.

Author: tjhorner

bot_test.go

@@ -549,9 +549,8 @@ func TestSendWithMediaGroup(t *testing.T) {
 	bot, _ := getBot(t)
 
 	cfg := tgbotapi.NewMediaGroup(ChatID, []interface{}{
-		tgbotapi.NewInputMediaPhoto("https://i.imgur.com/unQLJIb.jpg"),
-		tgbotapi.NewInputMediaPhoto("https://i.imgur.com/J5qweNZ.jpg"),
-		tgbotapi.NewInputMediaVideo("https://i.imgur.com/F6RmI24.mp4"),
+		tgbotapi.NewInputMediaPhoto("https://github.com/go-telegram-bot-api/telegram-bot-api/raw/0a3a1c8716c4cd8d26a262af9f12dcbab7f3f28c/tests/image.jpg"),
+		tgbotapi.NewInputMediaVideo("https://github.com/go-telegram-bot-api/telegram-bot-api/raw/0a3a1c8716c4cd8d26a262af9f12dcbab7f3f28c/tests/video.mp4"),
 	})
 	_, err := bot.Send(cfg)
 	if err != nil {