# File lib/bundler/settings.rb, line 13
    def []=(key, value)
      key = "BUNDLE_#{key.to_s.upcase}"
      @config[key] = value
      FileUtils.mkdir_p(config_file.dirname)
      File.open(config_file, 'w') do |f|
        f.puts @config.to_yaml
      end
      value
    end