build_gem

# File lib/bundler/gem_helper.rb, line 75
    def build_gem
      file_name = nil
      sh("gem build -V '#{spec_path}'") do
        file_name = File.basename(built_gem_path)
        SharedHelpers.filesystem_access(File.join(base, "pkg")) {|p| FileUtils.mkdir_p(p) }
        FileUtils.mv(built_gem_path, "pkg")
        Bundler.ui.confirm "#{name} #{version} built to pkg/#{file_name}."
      end
      File.join(base, "pkg", file_name)
    end