Replace deprecated FallingSand by new FallingBlock

src/main/java/com/sk89q/worldedit/bukkit/BukkitWorld.java

@@ -48,7 +48,7 @@ import org.bukkit.entity.Arrow;
 import org.bukkit.entity.Boat;
 import org.bukkit.entity.Entity;
 import org.bukkit.entity.ExperienceOrb;
-import org.bukkit.entity.FallingSand;
+import org.bukkit.entity.FallingBlock;
 import org.bukkit.entity.HumanEntity;
 import org.bukkit.entity.Item;
 import org.bukkit.entity.LivingEntity;
@@ -694,7 +694,7 @@ public class BukkitWorld extends LocalWorld {
                     ++num;
                 }
             } else if (type == EntityType.FALLING_BLOCKS) {
-                if (ent instanceof FallingSand) {
+                if (ent instanceof FallingBlock) {
                     ent.remove();
                     ++num;
                 }