Add missing import for SoundRepository

Author: valzargaming

src/Discord/Discord.php

@@ -39,6 +39,7 @@
 use Discord\Repository\GuildRepository;
 use Discord\Repository\LobbyRepository;
 use Discord\Repository\PrivateChannelRepository;
+use Discord\Repository\SoundRepository;
 use Discord\Repository\UserRepository;
 use Discord\Voice\Region;
 use Discord\Voice\VoiceClient;