v2.2.1: fixed crystal spire being vulernable to certain specific effects

core/src/main/java/com/shatteredpixel/shatteredpixeldungeon/actors/mobs/CrystalSpire.java

@@ -291,6 +291,11 @@ public class CrystalSpire extends Mob {
 		super.damage(dmg, src);
 	}
 
+	@Override
+	public boolean isInvulnerable(Class effect) {
+		return effect != Pickaxe.class;
+	}
+
 	@Override
 	public boolean add( Buff buff ) {
 		return false; //immune to all buffs and debuffs