Bossbar error

[z2vvqx]

Skellet isn't starting, it's red in the /plugins. Here's the error:

[05:32:46] [Server thread/INFO]: [Skellett] config.yml not found, generating a new config!
[05:32:46] [Server thread/INFO]: [Skellett] CustomEvents.yml not found, generating a new config!
[05:32:46] [Server thread/INFO]: [Skellett] Syntax.yml not found, generating a new file!
[05:32:46] [Server thread/INFO]: [Skellett] SyntaxToggles.yml not found, generating a new file!
[05:32:46] [Server thread/ERROR]: Error occurred while enabling Skellett v2.0.9 (Is it up to date?)
java.lang.NoClassDefFoundError: org/bukkit/boss/BarFlag
	at java.lang.Class.forName0(Native Method) ~[?:?]
	at java.lang.Class.forName(Class.java:398) ~[?:?]
	at ch.njol.skript.SkriptAddon.loadClasses(SkriptAddon.java:117) ~[?:?]
	at com.gmail.thelimeglass.Skellett.onEnable(Skellett.java:177) ~[?:?]
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:321) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:332) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:454) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at org.bukkit.craftbukkit.v1_8_R3.CraftServer.loadPlugin(CraftServer.java:393) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at org.bukkit.craftbukkit.v1_8_R3.CraftServer.enablePlugins(CraftServer.java:352) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at net.minecraft.server.v1_8_R3.MinecraftServer.s(MinecraftServer.java:439) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at net.minecraft.server.v1_8_R3.MinecraftServer.k(MinecraftServer.java:403) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at net.minecraft.server.v1_8_R3.MinecraftServer.a(MinecraftServer.java:358) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at net.minecraft.server.v1_8_R3.DedicatedServer.init(DedicatedServer.java:301) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:603) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at net.minecraft.server.v1_8_R3.MinecraftServer.lambda$spin$0(MinecraftServer.java:133) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at java.lang.Thread.run(Thread.java:829) [?:?]
Caused by: java.lang.ClassNotFoundException: org.bukkit.boss.BarFlag
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:92) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:87) ~[patched_1.8.8.jar:git-PandaSpigot-82]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:589) ~[?:?]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:522) ~[?:?]
	... 16 more```