title: Create-React-App: Runtime error - super() hasn't been called
body: <p>Updated create-react-app from 1.1.5 to 2.0.3
  Upgrade working fine and running locally with no errors.
  Building with no errors.
  For some reason I get the following error at runtime with my build:</p>
  
  <blockquote>
    <p>ReferenceError: this hasn't been initialised - super() hasn't been called</p>
  </blockquote>
  
  <p>The only thing that has changed in my package.json is my react script to 2.0.3. So guessing this could be possibly related updates to babel or webpack. 
  Anyone encountered an error similar to this?</p>