Merge pull request #108 from benjicarson/patch-1

impr: Favour hasMethod over method_exists

src/ItemPriceInfo.php

@@ -18,7 +18,7 @@ public function __construct(OrderItem $item)
         $this->item = $item;
         $this->quantity = $item->Quantity;
 
-        $originalprice = method_exists($item, 'DiscountableAmount') ?
+        $originalprice = $item->hasMethod('DiscountableAmount') ?
                             $item->DiscountableAmount() :
                             $item->UnitPrice();