message: Next screencast number was not displayed correctly in preview
  On each screencast page, the number for the next screencast was not displayed correctly, i.e. when on the page for screencast 001 the preview at the bottom showed the next screencast also as number 001, but should display 002 instead.
diff: <h2 class="text-center mb-small">Next up...</h2>
  <ScreencastPreview
  screencast={screencasts[screencast.nextScreencast]}
  - screencastNumber={screencast.nextScreencast}
  + screencastNumber={screencast.nextScreencast + 1}
  headlineOrder="h3"
  />
  </div>
  