In February, billionaire investor Warren Buffett announced that he was dropping 90 percent of his stock in Walmart. This is a grim prophecy for the retail juggernaut, which faces stiff competition in rival Amazon. Walmart, in addition to encouraging customers to order online and pick up in store, has recently announced the launch of a new online marketplace called “Store No. 8” in an effort to stay relevant in an increasingly digital marketplace. It’s common knowledge these days that ecommerce is...