Piedra, papel o tijera

Cada una de las dos entradas es "Rock", "Paper" o "Scissors". La piedra vence a las tijeras, las tijeras vencen al papel y el papel vence a la piedra. Devuelve "The winner is p1", "The winner is p2" o "It's a draw".

rps("Rock", "Paper") // "The winner is p2"
rps("Scissors", "Paper") // "The winner is p1"