Typo maybe? Add missing parenthesis

As solution for this line, I came up with the following:

```clojure
(= 2400 (reduce (fn [a b] (* a b))  (cons 100 [1 2 3 4])) (cond (>= 2 1) 2400  :else  [1 2 3 4]))
```

I was hopping to do something more simpler:

```clojure
(= 2400 (reduce (fn [a b] (* a b))  (cons 100  [1 2 3 4])))
```

... but it needs one more parenthesis at the end of line (three instead of two).

Maybe I am missing something, I recently started learning Clojure and I found your hosted Koans a good way to play and learn Clojure (Thanks!).