message: fix syntax error in conversation docs
diff: @@ -161,7 +161,7 @@ Developers can create complex conversational systems by combining these message
  From inside a prompt handler function, use `convo.gotoThread()` to instantly switch to a different part of the conversation. Botkit can be set to automatically navigate between threads based on user input, such as in the example below.
  ```javascript
  - let convo = new BotkitConversation(controller, 'cheese');
  + let convo = new BotkitConversation('cheese', controller);
  // create a path for when a user says YES
  convo.addMessage({
  