Update Stair.php to add use pocketmine\item\Tool;

Without this >= Tool::TIER_WOODEN does not work; so stone stairs do not give drops when broken. They also revert to not being broken on next connection.

src/pocketmine/block/Stair.php

@@ -22,6 +22,7 @@
 namespace pocketmine\block;
 
 use pocketmine\item\Item;
+use pocketmine\item\Tool;
 use pocketmine\math\AxisAlignedBB;
 use pocketmine\Player;
 
@@ -151,4 +152,4 @@ abstract class Stair extends Transparent{
 			return [];
 		}
 	}
-}
+}