feat(haskell): add prime number

haskell/8_prime_number.hs

@@ -0,0 +1,8 @@
+module IsPrime where
+
+isPrime :: Integer -> Bool
+isPrime x
+  | x `elem` [2, 3, 5, 7] = True
+  | x < 2 || even x = False
+  | otherwise = not $ any (\n -> x `rem` n == 0) [3, 5..last]
+  where last = (round . sqrt . fromIntegral) x