title: Send key doesn't trigger key up or key down
body: <p>Im sending keys to a input filter using sendkeys and supposed to be it will update the contents of the table, I check its screenshot and it placed the characters on the field. unfortunately after sendkeys, it doesnt trigger either keyup/keydown.</p>
  
  <p>How to trigger keyup or keydown on casper?</p>
  
  <p>Code:</p>
  
  <pre><code>this.sendKeys('input[name=\"filterString\"]', 'string');
  </code></pre>