bowling problem statement does not match code stub

**Requirements**

> Write code to keep track of the score of a game of bowling. It should support two operations:
>
> roll(pins : int) is called each time the player rolls a ball. The argument is the number of pins knocked down.
> score() : int is called only at the very end of the game. It returns the total score for that game.

But in reality:
```
score :: [Int] -> Either BowlingError Int
```