Add Modify Current Member Endpoint.php

https://discord.com/developers/docs/resources/guild#modify-current-member

Author: SQKo

src/Discord/Endpoint.php

@@ -112,6 +112,8 @@ class Endpoint
     // GET, PATCH, PUT, DELETE
     public const GUILD_MEMBER = self::GUILD.'/members/:user_id';
     // PATCH
+    public const GUILD_MEMBER_SELF = self::GUILD.'/members/@me';
+    // PATCH
     public const GUILD_MEMBER_SELF_NICK = self::GUILD.'/members/@me/nick';
     // PUT, DELETE
     public const GUILD_MEMBER_ROLE = self::GUILD.'/members/:user_id/roles/:role_id';