message: Update demo.js (fixing blog URL)
diff: @@ -28,7 +28,7 @@ const Background = props => {
  <Block.Paragraph>
  Watch the videos below to get an introduction to Backstage and
  to see how we use different plugins to customize {' '}
  - <a href="https://labs.spotify.com/2020/04/21/how-we-use-backstage-at-spotify/">
  + <a href="https://engineering.atspotify.com/2020/04/21/how-we-use-backstage-at-spotify/">
  our internal version of Backstage at Spotify
  </a>
  .
  