Meredith Woerner Deputy Editor, Variety.comSPOILER ALERT: Do not read if you have not yet watched “World’s Toughest Race: Eco-Challenge Fiji,” streaming now on Amazon.The 11 day, 416-mile “world’s toughest race” is back. After an 18-year hiatus realty tv mastermind Mark Burnett resurrected the “Eco-Challenge” for new audiences on Amazon Prime Video.