By Simon Jessop and Ross Kerber LONDON (Reuters) -Amazon.com Inc., the world’s biggest retailer, will face a shareholder vote calling for an independent audit of its treatment of warehouse workers after the top U.S. securities regulator turned down the company’s request to skip the resolution. The decision means Amazon investors will get to vote on the issue for the first time, proponents said, taking advantage of guidance from the U.S. Securities and Exchange Commission in November that made it more supportive of votes on significant social issues. Founded by billionaire Jeff Bezos, Amazon ha…