1.13 support

[literalplus]

Describe the bug
The configuration command does not work with 1.13.

To Reproduce
Steps to reproduce the behavior:

1. Install a Spigot 1.13 server
2. Issue the /cbu command
3. Observe stack trace in console

Expected behavior
No stack trace, command works.

Environment (please complete the following information):

• Platform: Spigot
• Platform version: git-Spigot-69774b3-ec2095d (MC: 1.13) (Implementing API version 1.13-R0.1-SNAPSHOT)
• CBU version: 1.5.6-SNAPSHOT

Relevant server logs

>cbu
[02:23:49 WARN]: Unexpected exception while parsing console command "cbu"
org.bukkit.command.CommandException: Unhandled exception executing command 'cbu' in plugin CommandBlockerUltimate v1.5.6-SNAPSHOT
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at org.bukkit.craftbukkit.v1_13_R1.CraftServer.dispatchCommand(CraftServer.java:693) ~[spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at org.bukkit.craftbukkit.v1_13_R1.CraftServer.dispatchServerCommand(CraftServer.java:678) [spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at net.minecraft.server.v1_13_R1.DedicatedServer.aW(DedicatedServer.java:453) [spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at net.minecraft.server.v1_13_R1.DedicatedServer.w(DedicatedServer.java:412) [spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at net.minecraft.server.v1_13_R1.MinecraftServer.v(MinecraftServer.java:819) [spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at net.minecraft.server.v1_13_R1.MinecraftServer.run(MinecraftServer.java:717) [spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at java.lang.Thread.run(Thread.java:844) [?:?]
Caused by: java.lang.VerifyError: Cannot inherit from final class
	at java.lang.ClassLoader.defineClass1(Native Method) ~[?:?]
	at java.lang.ClassLoader.defineClass(ClassLoader.java:1009) ~[?:?]
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:174) ~[?:?]
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:150) ~[spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at org.bukkit.plugin.java.JavaPluginLoader.getClassByName(JavaPluginLoader.java:193) ~[spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:111) ~[spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:100) ~[spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:566) ~[?:?]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:499) ~[?:?]
	at li.l1t.common.command.BukkitExecutionExecutor.onCommand(BukkitExecutionExecutor.java:47) ~[?:?]
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot-1.13.jar:git-Spigot-69774b3-ec2095d]
	... 8 more