A trader works on the floor of the New York Stock Exchange during the afternoon of December 4, 2015 in New York City.Andrew Burton/Getty ImagesSmall caps are making a comeback as a September rate cut seems increasingly likely.But invest in high-quality individual stocks, not broad indexes, according to Greg Tuorto.Tuorto is a portfolio manager at Goldman Sachs Asset Management.After over two years of underperformance, it seems like small-cap stocks are finally poised to take off.