add missing @Override annotation to item's toString

Java/com/gildedrose/Item.java

@@ -14,7 +14,8 @@ public class Item {
         this.quality = quality;
     }
 
-    public String toString() {
+   @Override
+   public String toString() {
         return this.name + ", " + this.sellIn + ", " + this.quality;
     }
 }