fix: sentence fix (remove a period)

Author: AmiyahJo

lesson_14/exceptions/exceptions_app/src/main/java/com/codedifferently/lesson14/ecommerce/EcommerceSystem.java

@@ -20,7 +20,7 @@ public void addProduct(String productId, String name) {
   public String placeOrder(String productId, int quantity) throws ProductNotFoundException {
     Product product = products.get(productId);
     if (product == null) {
-      throw new ProductNotFoundException("Product with ID " + productId + " not found.");
+      throw new ProductNotFoundException("Product with ID " + productId + " not found");
     }
     String orderId = UUID.randomUUID().toString();
     orders.put(orderId, new Order(orderId, product, quantity));