accept IO in audit/scanner.rb
alias `UnpatchedGem#gem` as `UnpatchedGem#rubygem`.

Kernel#gem is a method rubygems adds already to specify what version
of a gem you want to load alongside the requirements("~> 0.5").

Scanner::UnpatchedGem#gem conflicts with that method name so
the `#rubygem` alias is provided as an alternative.