Update XML Namespace URI for KML

The XML Namespace http://earth.google.com/kml/2.2 returns a 404,
as do other similar Google URIs for KML 2.2.  This causes the output
not to validate.  Changed to http://www.opengis.net/kml/2.2
Merge pull request #1 from kjkjava/fix-kml-xmlns

Update XML Namespace URI for KML