Don't bundle code with own version of ruby-nessus gem

[xntrik]

Currently, the ruby-nessus gem doesn't have the ability to extract critical findings. I've had a push merged into the code-base, but, unsure if the actual gem has been updated.

As soon as that gem is published, I can update this gem to remove the internal copy - and just include the dep in the gemspec.

This will reduce the code slightly.