Adds missing xsl namespace
Adds missing xsl namespace

Namespace php was not defined in docblock xsl. This caused critical errors
during processing the template. Resulting in an empty api-doc. Namespace is required
to be able to use the php: prefix.

fixes #1756

rgeraads/phpDocumentor2,rgeraads/phpDocumentor2,mbed67/phpDocumentor2,jaapio/phpDocumentor2,phpDocumentor/phpDocumentor2,mbed67/phpDocumentor2,mbed67/phpDocumentor2,rgeraads/phpDocumentor2,phpDocumentor/phpDocumentor2,jaapio/phpDocumentor2,rgeraads/phpDocumentor2,phpDocumentor/phpDocumentor2,jaapio/phpDocumentor2,jaapio/phpDocumentor2,mbed67/phpDocumentor2,phpDocumentor/phpDocumentor2