title: ReactJS tutorial: does not display the expected unique key warning
body: <p>I'm new to ReactJS and I'm trying to follow the tutorial here: <a href="https://reactjs.org/tutorial/tutorial.html" rel="nofollow noreferrer">https://reactjs.org/tutorial/tutorial.html</a> . Everything seems fine except at this step: <a href="https://reactjs.org/tutorial/tutorial.html#picking-a-key" rel="nofollow noreferrer">https://reactjs.org/tutorial/tutorial.html#picking-a-key</a> where it says</p>
  <blockquote>
  <p>For now, we should see a list of the moves that have occurred in the game and a warning that says:</p>
  <blockquote>
  <p>Warning: Each child in an array or iterator should have a unique “key” prop. Check the render method of “Game”.</p>
  </blockquote>
  </blockquote>
  <p>I've set up my project using create-react-app (following the instructions here: <a href="https://reactjs.org/tutorial/tutorial.html#setup-option-2-local-development-environment" rel="nofollow noreferrer">https://reactjs.org/tutorial/tutorial.html#setup-option-2-local-development-environment</a>), did not change any settings, yet for some reason at this step (before a key is added to the li element) when I run &quot;npm start&quot;, I don't see the said warning.</p>
  <p>I've tried googling for the answer, ironically all the results I've found are people asking how to get rid of this warning, whereas I'm trying to see this warning. Does anyone know what could be happening here?</p>
  <p>Thanks in advance!</p>