#39 Updated test to use XHTML since Saxon doesn't support HTML 1.0

@yegor256 , JSoup is producing valid HTML at this point; except Saxon doesn't support HTML 1.0 and needs XHTML instead. Seems like a limitation of our own `XhtmlMatchers` API and not of JSoup. See: http://p2p.wrox.com/xslt/49371-error-saxon-8-8-a.html