IslandWorldChallenges error

[14:27:15] [Server thread/ERROR]: Error occurred while enabling IslandWorldChallenges v1.4 (Is it up to date?)
java.lang.NoSuchMethodError: org.bukkit.configuration.file.YamlConfiguration.loadConfiguration(Ljava/io/InputStream;)Lorg/bukkit/configuration/file/YamlConfiguration;
	at pl.iwc.IWChallenges.loadMessages(IWChallenges.java:1021) ~[?:?]
	at pl.iwc.IWChallenges.onEnable(IWChallenges.java:87) ~[?:?]
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264) ~[spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:337) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:402) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugin(CraftServer.java:380) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugins(CraftServer.java:329) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at net.minecraft.server.v1_12_R1.MinecraftServer.t(MinecraftServer.java:422) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at net.minecraft.server.v1_12_R1.MinecraftServer.l(MinecraftServer.java:383) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at net.minecraft.server.v1_12_R1.MinecraftServer.a(MinecraftServer.java:338) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at net.minecraft.server.v1_12_R1.DedicatedServer.init(DedicatedServer.java:272) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:545) [spigot-1.12.1.jar:git-Spigot-65e8124-79e55b6]
	at java.lang.Thread.run(Unknown Source) [?:1.8.0_144]