hixie: typo (whatwg r5820)

hixie: typo (whatwg r5820)

http://dev.w3.org/cvsweb/html5/spec/Overview.html?r1=1.4678&r2=1.4679&f=h
http://html5.org/tools/web-apps-tracker?from=5819&to=5820

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RCS file: /sources/public/html5/spec/Overview.html,v
retrieving revision 1.4678
retrieving revision 1.4679
diff -u -d -r1.4678 -r1.4679
--- Overview.html	3 Feb 2011 20:54:22 -0000	1.4678
+++ Overview.html	3 Feb 2011 20:56:35 -0000	1.4679
@@ -2308,7 +2308,7 @@
 
    <dt><cite>Polyglot Markup: HTML-Compatible XHTML Documents</cite> <a href="#refsPOLYGLOT">[POLYGLOT]</a></dt>
 
-   <dd><blockquote><p>A document that uses polyglot markup is document
+   <dd><blockquote><p>A document that uses polyglot markup is a document
    that is a stream of bytes that parses into identical document trees
    (with the exception of the xmlns attribute on the root element)
    when processed as HTML and when processed as XML. Polyglot markup