title: Vorpal Vantage: i'm not able to exit the interactive console programmatically
body: <p>What's wrong with this?</p>
  
  <pre><code>const Vantage = require('vantage')
  
  const v = Vantage()
      .delimiter('$test')
      .listen(9000)
      .show()
  
  const close = () =&gt; {
      v.exec('exit', () =&gt; {
          console.log('DONE')
      })
   }  
  setTimeout(close, 1000)
  </code></pre>
  
  <p>Error:</p>
  
  <blockquote>
    <p>UI Prompt called when already mid prompt. at Object.prompt
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/node_modules/vorpal/lib/ui.js:131:13)
    at Vorpal.vorpal.prompt
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/node_modules/vorpal/lib/vorpal.js:450:8)
    at Vorpal.vorpal.exit
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/node_modules/vorpal/lib/vorpal.js:1160:12)
    at Session.
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/node_modules/vorpal/lib/vorpal-commons.js:49:19)
    at Vorpal.vorpal._exec
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/node_modules/vorpal/lib/vorpal.js:846:18)
    at Vorpal.vorpal._execQueueItem
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/node_modules/vorpal/lib/vorpal.js:594:10)
    at Vorpal.vorpal._queueHandler
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/node_modules/vorpal/lib/vorpal.js:579:10)
    at Vorpal.vorpal.exec
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/node_modules/vorpal/lib/vorpal.js:554:24)
    at Timeout.close [as _onTimeout]
    (/Users/giggioz/Spaghetti/keeper/keeper-giochipiu-delegates/xxx.js:9:7)
    at ontimeout (timers.js:380:14)</p>
  </blockquote>