fixed friend serialization

Author: emyfops

src/main/kotlin/com/lambda/friend/FriendManager.kt

@@ -41,7 +41,7 @@ import java.util.*
 //  - Improve save file structure.
 object FriendManager : Configurable(FriendConfig), Loadable {
     override val name = "friends"
-    val friends by setting("friends", emptySet<GameProfile>())
+    val friends by setting("friends", emptySet<GameProfile>(), serialize = true)
 
     fun befriend(profile: GameProfile) = friends.add(profile)
     fun unfriend(profile: GameProfile): Boolean = friends.remove(profile)