Update BatchUtil.cs
Update BatchUtil.cs

fix bugs   
before :  
      we can only use
      context.Items.Where(a => a.ItemId <= 500).BatchUpdate(a => new Item { Quantity = a.Quantity + 100 });
now : we can use 
          int quantity =100
          context.Items.Where(a => a.ItemId <= 500).BatchUpdate(a => new Item { Quantity = a.Quantity + quantity });
---              
          string description="good"
           var item=new Item();
          context.Items.Where(a => a.ItemId <= 500).BatchUpdate(a => new Item { Description=description + a.Description + item.Name + + DateTime.Now.Tostring()});
borisdj/EFCore.BulkExtensions