message: Fixing typo : covo --> convo
diff: @@ -673,7 +673,7 @@ conversation.
  ```javascript
  // create an end state thread
  -covo.addMessage('This is the end!', 'the_end');
  +convo.addMessage('This is the end!', 'the_end');
  // now transition there with a nice message
  convo.transitionTo('the_end','Well I think I am all done.');
  