Sell in May and go away? Not with this summer’s hot action. In August, investors dumped ETFs that short the stock market — and picked up a healthy shot of gains from biotechnology funds. First Trust NYSE Arca Biotech (FBT) popped 14% to an all-time high last month, outperforming all nonleveraged ETFs. It has rocketed 57% from a 52-week low of 59.09 amid a brightening sector outlook.