Made zombie invasions fire CreatureSpawn event. Fixes BUKKIT-1090

By: EvilSeph <evilseph@gmail.com>

paper-api/src/main/java/org/bukkit/event/entity/CreatureSpawnEvent.java

@@ -128,6 +128,10 @@ public class CreatureSpawnEvent extends EntityEvent implements Cancellable {
          * When an iron golem is spawned to defend a village
          */
         VILLAGE_DEFENSE,
+        /**
+         * When a zombie is spawned to invade a village
+         */
+        VILLAGE_INVASION,
         /**
          * When a creature is manually spawned
          */