```ruby
require "boxen/preflight"

class Boxen::Preflight::OS < Boxen::Preflight
  def ok?
    `sw_vers -productVersion`.start_with? "10.8"
  end

  def run
    abort "You must be running OS X 10.8 (Mountain Lion)."
  end
end
```

Add 10.9 to list of supported OS X releases
user
```ruby
require "boxen/preflight"

class Boxen::Preflight::OS < Boxen::Preflight
  SUPPORTED_RELEASES = %w(10.8 10.9)

  def ok?
    osx? && supported_release?
  end

  def run
    abort "You must be running one of the following OS X versions: #{SUPPORTED_RELEASES.join(' ')}."
  end

  private

  def osx?
    `uname -s` == "Darwin"
  end

  def supported_release?
    SUPPORTED_RELEASES.any? do |r|
      current_release.starts_with? r
    end
  end

  def current_release
    @current_release ||= `sw_vers -productVersion`
  end
end
```
assistant