title: codeceptJS / webdriverIO exits script with grab commands
body: <p>I'm new to codeceptJS but best I can tell it simply does not work with yield.</p>
  
  <pre><code>'use strict';
  Feature('Testing Begins');
  Before((I) =&gt; {
    I.resizeWindow(1500, 1000);
    I.amOnPage('http://absolutenet.com');
  });
  
  Scenario('ANI testing', function*(I){
    I.waitForText('bring your site to life');
    I.amOnPage('http://www.absolutenet.com/');
    let title = yield I.grabTitle();
    console.info(title);
    I.see('bogus text that is not there');
  });
  </code></pre>
  
  <p>I have tried several of the grab commands as well as executeScript. I know the commands are working because for some reason one or two lines do execute after the yield so I can output the variable I am assigning. However, I can never use it because the browser closes and the script terminates. Even worse, I can put in a test that is obviously invalid (I.see('some bogus non existent text');) and the Scenario exits with a Success!</p>
  
  <p>The above is live so you can execute it to see the problem. Testing with Linux and FireFox if that matters.</p>
  
  <p>Can anyone give me an example of how to use yield and continue the test? </p>
  
  <p>UPDATE: The developer says this is a bug and it will be fixed soon.</p>