title: commander.js: passing isDefault option for command with action()
body: <p>As per the <a href="https://github.com/tj/commander.js/" rel="noreferrer">commander.js</a> readme, I can specify the default command thus:</p>
  
  <pre><code>var program = ...;
  
  program
    ...
    .command('list', 'list packages installed', {isDefault: true})
    .parse(process.argv);
  </code></pre>
  
  <p>In my application, I'm using the <code>.command()</code> without the description parameter, for using <code>.action()</code>. I tried passing the second param <code>null</code> and the third option with the <code>isDefault:true</code>. But it does not seem to work:</p>
  
  <pre><code>program.command('help', null, {isDefault:true})
    .description('display help information.')
    .action(function(){
      program.outputHelp();
    });
  </code></pre>
  
  <p>How do I pass <code>isDefault:true</code> to a command with <code>.action()</code>?</p>