version_reporter.rb

# An example Jekyll generator. Utilizes the new plugin system.
#
# 1. Make a _plugins directory in your jekyll site, and put this class in a file there.
# 2. Upon site generation, version.html will be created in your root destination with
# #  the version of Jekyll that generated it

module Jekyll
  class VersionReporter < Generator
    safe true

    def generate(site)
      File.open(File.join(site.config["destination"], 'version.html'), 'w') do |f|
        f.write(generate_report(site))
      end
    end

    private

    def generate_report(site)
      "Site generated with Jekyll version: #{Jekyll::VERSION}"
    end

  end
end

Changing the site.config["destination"] to site.source fixed this for me.

create version.html in your root develop folder , fixed.
Jekyll version: 2.5.3

this plugin does not run for me

jekyll 3.1.6 | Error:  No such file or directory @ rb_sysopen _site/version.html