Initial commit

Rock paper scissors, does a single iteration of a rock paper scissors
game. Displays the computer's move and the winner of the game.
You're right that the `.last` makes this fragile. However, there's a good fix: `@defeaters[@computer_move]`. `@defeaters.assoc` converts the hash to an array - instead, you can use `[...]` to index into the hash and keep using the hash.