Nokogiri Parser should strip xml before parsing

[aselder]

The nokogiri parser checks if the stripped xml is empty before parser, but passes the unstripped XML to the parser.

This means the you have to strip it yourself before passing to the parser, which means the strip in the guard clause is unnecessary.

A better and more robust solution is for the Nori parse method to strip the xml before passing to Nokogiri.

I'll throw together a quick pull request.

[rubiii]

please do.