Fix doctests-posix

hpath.cabal

@@ -76,7 +76,8 @@ test-suite doctests-posix
                      hpath,
                      doctest >= 0.8,
                      HUnit,
-                     QuickCheck
+                     QuickCheck,
+                     word8
 
 test-suite spec
   if os(windows)

src/System/Posix/FilePath.hs

@@ -96,6 +96,7 @@ import           Control.Arrow (second)
 -- $setup
 -- >>> import Data.Char
 -- >>> import Data.Maybe
+-- >>> import Data.Word8
 -- >>> import Test.QuickCheck
 -- >>> import Control.Applicative
 -- >>> import qualified Data.ByteString as BS