Traverse.hs: substitute NBSP (0xC2 0xA0) to SP (0x20)

Before patching ./setup haddock failed to parse some comments:

     100% (  3 /  3) in 'System.Directory.Layout.Internal'
    doc comment parse failed:  Make layout as specified

     For example, suppose you are in an empty directory

     @
     % tree
     .
     @

After patch everything renders correctly.

Haddock-bug: http://trac.haskell.org/haddock/ticket/250
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>