Doesn't work and gives out a mistake:
06.11 22:54:41 [Server] INFO [22:54:41 WARN]: [ProjectKorra] Task #45 for ProjectKorra v1.5 generated an exception
06.11 22:54:41 [Server] INFO java.lang.NoSuchMethodError: java.util.concurrent.ConcurrentHashMap.keySet()Ljava/util/concurrent/ConcurrentHashMap$KeySetView;
06.11 22:54:41 [Server] INFO at ca.carbogen.korra.LavaSlap.LavaSlap.progressAll(LavaSlap.java:297) ~[?:?]
06.11 22:54:41 [Server] INFO at ca.carbogen.korra.LavaSlap.LavaSlapListener$1.run(LavaSlapListener.java:70) ~[?:?]
06.11 22:54:41 [Server] INFO at org.bukkit.craftbukkit.v1_7_R2.scheduler.CraftTask.run(CraftTask.java:58) ~[spigot.jar:git-Spigot-1370]
06.11 22:54:41 [Server] INFO at org.bukkit.craftbukkit.v1_7_R2.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345) [spigot.jar:git-Spigot-1370]
06.11 22:54:41 [Server] INFO at net.minecraft.server.v1_7_R2.MinecraftServer.v(MinecraftServer.java:618) [spigot.jar:git-Spigot-1370]
06.11 22:54:41 [Server] INFO at net.minecraft.server.v1_7_R2.DedicatedServer.v(DedicatedServer.java:273) [spigot.jar:git-Spigot-1370]