OMAHA, Neb. (Reuters) - Warren Buffett’s Berkshire Hathaway Inc on Saturday swung to a big quarterly profit, bolstered by gains in its stock investments, and also posted a small increase in operating earnings. FILE PHOTO: Warren Buffett, CEO of Berkshire Hathaway Inc, at the company annual meeting weekend in Omaha, Nebraska U.S. May 6, 2018.…