The Latin American online bank is growing at a rapid pace.Nu Holdings (NU 4.01%) is a Brazil-based digital bank operating under the banner NuBank. It operates in three Latin American countries, so it might not be on your radar. But if you're an investor, it should be. It's growing by leaps and bounds, and its stock has gained accordingly. Can it be part of a millionaire-maker portfolio?The bank customers have been waiting forBanking is an age-old business, but digital banks have been upending the industry w ...