Correct Problem3.hs to use the new type for `primes`.

Problem3.hs

@@ -1,7 +1,7 @@
 -- What is the largest prime factor of the number 600851475143 ?
 import Euler
 
-factors n = go (primes ()) n
+factors n = go primes n
    where go (p:ps) n | n < p          = []
                      | n `mod` p == 0 = p : go (p:ps) (n `div` p)
                      | otherwise      = go ps n