Fix RPKit Locks integration failing due to abstract method error.

[dmccoystephenson]

Error Output

22:47:44 ERROR]: Error occurred while enabling MedievalFactions v5.3.0-SNAPSHOT (Is it up to date?)
java.lang.AbstractMethodError: Receiver class com.dansplugins.factionsystem.locks.MfRpkLockService does not define or inherit an implementation of the resolved method 'abstract com.rpkit.core.plugin.RPKPlugin getPlugin()' of interface com.rpkit.core.service.Service.
at com.rpkit.core.bukkit.service.BukkitServicesDelegate.set(BukkitServicesDelegate.kt:32) ~[?:?]
at com.rpkit.core.service.Services.set(Services.kt:26) ~[?:?]
at com.dansplugins.factionsystem.locks.MfRpkLockService.(MfRpkLockService.java:26) ~[?:?]
at com.dansplugins.factionsystem.MedievalFactions.setupRpkLockService(MedievalFactions.kt:521) ~[?:?]
at com.dansplugins.factionsystem.MedievalFactions.onEnable(MedievalFactions.kt:233) ~[?:?]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264) ~[spigot-api-1.18.2-R0.1-SNAPSHOT.jar:?]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:342) ~[spigot-api-1.18.2-R0.1-SNAPSHOT.jar:?]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:480) ~[spigot-api-1.18.2-R0.1-SNAPSHOT.jar:?]
at org.bukkit.craftbukkit.v1_18_R2.CraftServer.enablePlugin(CraftServer.java:518) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at org.bukkit.craftbukkit.v1_18_R2.CraftServer.enablePlugins(CraftServer.java:432) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.loadWorld0(MinecraftServer.java:612) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.loadLevel(MinecraftServer.java:414) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.dedicated.DedicatedServer.e(DedicatedServer.java:263) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:1007) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.lambda$0(MinecraftServer.java:304) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at java.lang.Thread.run(Thread.java:833) [?:?]