Update to metasploit_data_models 0.6.1

MetasploitDataModels 0.6.1 adds a re-usable yard.rake so that all
Metasploit project don't have to define their own.  It also adds guards
so that the YARD tasks aren't defined (and don't cause errors) if YARD
is not available.

This also adds support for making the Rakefile work with `bundle install
--without development test` so it still functions in the bundle building
environment for Pro.