fix cancellation model to receive id also as string

Riskified.SDK/Model/OrderCancellation.cs

@@ -22,6 +22,22 @@ public OrderCancellation(int merchantOrderId, DateTime cancelledAt, string cance
             CancelReason = cancelReason;
         }
 
+        /// <summary>
+        /// Creates an order cancellation
+        /// </summary>
+        /// <param name="merchantOrderId">The unique id of the order at the merchant systems</param>
+        /// <param name="cancelledAt">The date and time when the order was cancelled (optional)</param>
+        /// <param name="cancelReason">If the order was cancelled, the value will be one of the following:
+        /// "customer": The customer changed or cancelled the order.
+        /// "fraud": The order was fraudulent.
+        /// "inventory": Items in the order were not in inventory.
+        /// "other": The order was cancelled for a reason not in the list above. </param>
+        public OrderCancellation(string merchantOrderId, DateTime cancelledAt, string cancelReason) : base(merchantOrderId)
+        {
+            CancelledAt = cancelledAt;
+            CancelReason = cancelReason;
+        }
+
         public override void Validate(Validations validationType = Validations.Weak)
         {
             base.Validate(validationType);