SPIGOT-2381: Use custom spawnreason for dropItem

src/main/java/org/bukkit/craftbukkit/CraftWorld.java

@@ -328,7 +328,7 @@ public class CraftWorld implements World {
         Validate.isTrue(item.getTypeId() != 0, "Cannot drop AIR.");
         EntityItem entity = new EntityItem(world, loc.getX(), loc.getY(), loc.getZ(), CraftItemStack.asNMSCopy(item));
         entity.pickupDelay = 10;
-        world.addEntity(entity);
+        world.addEntity(entity, SpawnReason.CUSTOM);
         // TODO this is inconsistent with how Entity.getBukkitEntity() works.
         // However, this entity is not at the moment backed by a server entity class so it may be left.
         return new CraftItem(world.getServer(), entity);