def gemspec_filename(gem_version = nil)
      gem_version ||= version.to_s
      n = [name, gem_version]
      n.push(@platform) if @platform != 'ruby'
      "#{n.join('-')}.gemspec.rz"
    end
def gemspec_filename(gem_version = nil)
      gem_version ||= version.to_s
      n = [name, gem_version]
      n.push(@platform) if @platform != 'ruby'
      "#{n.join('-')}.gemspec.rz"
    end
Returns the filename of the gemspec file.

 @param [String] gem_version
 @return [String]