Add phone-number test (input too long)

No tests checked for inputs longer than 11 digits. A correct solution should be 10 or 11 digits.

The following solution passed with before this change. The new test detects the error.

```haskell
module Phone (areaCode, number, prettyPrint) where

import Data.Char (isDigit)

number :: String -> String
number = cleanup . digits
  where
    digits = filter isDigit
    cleanup n = case compare (length n) 10 of
      EQ -> n
      GT | head n == '1' -> tail n
      _ -> replicate 10 '0'

areaCode :: String -> String
areaCode = take 3 . number


prettyPrint :: String -> String
prettyPrint n = "(" ++ areaCode n ++ ") "
                ++ prefix cleaned ++ "-"
                ++ suffix cleaned
  where
    cleaned = number n
    prefix = take 3 . drop 3
    suffix = take 4 . drop 6
```
Merge pull request #38 from sirreal/patch-1

Add phone-number test (input too long)