Rivers Casino in Des Plaines has begun renovations to its existing space, company officials said Thursday, ahead of further expansion plans being made in the wake of the new state gambling law. The casino -- the state's largest and most lucrative -- is applying for a sports betting license and already started work to convert its Cube lounge to an official sportsbook that could open by the end of the year, said Bill Carstanjen, CEO of Churchill Downs Inc.