Fix import that went missing during cherry-pick

Author: duncte123

src/main/kotlin/dev/arbjerg/lavalink/client/LavalinkNode.kt

@@ -26,6 +26,7 @@ import reactor.kotlin.core.publisher.toMono
 import java.io.Closeable
 import java.io.IOException
 import java.time.Duration
+import java.util.Collections
 import java.util.concurrent.ConcurrentHashMap
 import java.util.concurrent.TimeUnit
 import java.util.function.Consumer