Fix the documentation build failure (wrong texinfo).

Fix the documentation build failure (wrong texinfo).

Building PDF, PostScript, and DVI versions of the documentation fails
with the following error message(s):
../../doc/cln.texi:1170: Argument of @asis has an extra }.
<inserted text>
                @par
<to be read again>
                   }
According to texinfo maintainer @itemize @asis is illegal, one should
use @itemize @w{} instead.
See <http://lists.gnu.org/archive/html/bug-texinfo/2009-03/msg00016.html>.