This story was originally published on CFO.com. To receive daily news and insights, subscribe to our free daily CFO.com newsletter. Amazon’s recently reported plans to offer “ultrafast” grocery delivery may well have been a shot across the bow at Instacart, which has carved a lucrative niche in the space. The e-commerce giant’s plans to deliver groceries in 30 minutes or less sent Instacart’s stock tumbling 5% earlier this month. But the grocery delivery company so far appears to be taking it all in stri ...