I missed a spot where I referenced the nested_paths as nested_pathnams
after I renamed the variable. Now, Msf::ModuleManager#add_module_paths
has rspec tests.
Rspec can be invoked with `rake` as the default task or `rake spec`
explicitly.
I changed RuntimeError to ArgumentError since that error was more
specific to having a bad argument error. I adding missing dependencies
to the Gemfile and a require to msf/core/db_manager.rb where it errored
out trying to access Msf::Config when I just did require 'msf/core' in
the spec.