Update current library to V3 API.

[cgome032]

ESPN's existing fantasy footbal endpoint has changed from V2 to the V3 API endpoint.

Update the existing library to pull information from the new V3 endpoint instead of the older V2 endpoint. There are now two endpoints to pull league information from ESPN.
CURRENT_ENDPOINT: https://fantasy.espn.com/apis/v3/games/FFL/seasons/{year}/segments/0/leagues/{league_id}
HISTORICAL_ENDPOINT: https://fantasy.espn.com/apis/v3/games/ffl/leagueHistory/{league_id}?seasonId={season_id}