title: node commander options are undefined
body: <p>I'm having trouble using commander:
  <a href="https://github.com/tj/commander.js/" rel="nofollow">https://github.com/tj/commander.js/</a></p>
  
  <pre><code>program
      .command('school')
      .arguments("&lt;year&gt;")
      .option("--month &lt;month&gt;", "specify month")
      .parse(process.argv)
      .action(function (year) {
          console.log(`the year is ${year} and the month is ${program.month}`);
      });
  </code></pre>
  
  <p>I don't know why but <code>program.month</code> is undefined even when i run with <code>--month 12</code>.</p>
  
  <p>Thanks in advance.</p>