Transition group example for ternaries

The example for transition group to animate in/out elements is with an array. I haven't had time to dig into the code but are we not able to use a ternary?

```js
<TransitionGroup>
  { isFirstItemVisible ? (
      <CSSTransition>
         ...
      </CSSTransition>
  ) : (
      <CSSTransition>
         ...
      </CSSTransition>
  )}
</TransitionGroup
```
