Add api version to prevent legacy data loading

bukkit/src/main/resources/plugin.yml

@@ -2,6 +2,7 @@ name: ViaBackwards
 version: ${project.version}
 description: Allow older Minecraft versions to connect to a newer server version.
 main: nl.matsv.viabackwards.BukkitPlugin
+api-version: 1.13
 
 authors: [Matsv, KennyTV, Gerrygames, creeper123123321, ForceUpdate1]
 website: ${project.url}