bpo-32800: Update link to w3c doc for xml default namespaces (GH-5609) (GH-5613)

The new link is given in a red box on the old page.
(cherry picked from commit 8d1f2f40)
Co-authored-by: sblondon <sblondon@users.noreply.github.com>

Doc/library/xml.etree.elementtree.rst

@@ -274,7 +274,7 @@ If the XML input has `namespaces
 with prefixes in the form ``prefix:sometag`` get expanded to
 ``{uri}sometag`` where the *prefix* is replaced by the full *URI*.
 Also, if there is a `default namespace
-<https://www.w3.org/TR/2006/REC-xml-names-20060816/#defaulting>`__,
+<https://www.w3.org/TR/xml-names/#defaulting>`__,
 that full URI gets prepended to all of the non-prefixed tags.
 
 Here is an XML example that incorporates two namespaces, one with the

Misc/NEWS.d/next/Documentation/2018-02-10-15-16-04.bpo-32800.FyrqCk.rst

+Update link to w3c doc for xml default namespaces.