title: React-hot-loader: react--dom patch is not detected
body: <p>I updated some npm packages in my Gatsby project and now I'm seeing this warning in console:</p>
  
  <p><code>React-hot-loader: react--dom patch is not detected. React 16.6+ features may not work.</code></p>
  
  <p>However, when I look into the source code, there is a comment:</p>
  
  <p><code>// Actually everything works...</code></p>
  
  <p>What does this warning actually mean? Is this something I should fix or just let it be?</p>