message: docs: fix ng-for link in structural-directives.md
  Correctly the reference to ng-for as `NgForOf` so that we get the word linked to the API page.
  `NgFor` is not a JavaScript symbol so the docs infra doesn't autolink to the API page unless
  we use the correct symbol name - `NgForOf`.
  PR Close
diff: @@ -8,7 +8,7 @@ For the example application that this page describes, see the <live-example></li
  </div>
  -For more information on Angular's built-in structural directives, such as `NgIf`, `NgFor`, and `NgSwitch`, see [Built-in directives](guide/built-in-directives).
  +For more information on Angular's built-in structural directives, such as `NgIf`, `NgForOf`, and `NgSwitch`, see [Built-in directives](guide/built-in-directives).
  {@a unless}
  