def output_pdf(html, filename)
      args = command(filename)
      invoke = args.join(' ')

      IO.popen(invoke, "wb+") do |pdf|
        pdf.puts(html)
        pdf.close_write
        pdf.gets(nil)
      end
    end
def output_pdf(html, filename)
      args = command(filename)
      invoke = args.join(' ')

      IO.popen(invoke, "wb+") do |pdf|
        pdf.puts(html)
        pdf.close_write
        pdf.gets(nil)
      end
    end
Set up options for wkhtmltopdf
 @param [String] parameters
 Convert the html to pdf and write it to file
 @param [String] html the html input
 @param [String] filename the name of the output file