doc: fix formatting in LICENSE for RTF generation

Current format does not render properly when converted to RTF by
the tools/license2rtf.js tool, specifically the wrong sections are
presented as bold, giving the wrong emphasis to the document.

This fix makes the formatting more consistent, with non-license
summary sections bold and the licenses themselves unformatted.

PR: https://github.com/iojs/io.js/pull/436


Reviewed-by: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-by: Bert Belder <bertbelder@gmail.com>