Update example to have proper ctrl

[bsiddiqui]

Currently the html includes MainCtrl but the js defines ScrollCtrl. I updated the example so they match.

[mary-poppins]

Thanks for the PR!

• Contributor signed CLA now or in the past
  • If you just signed, leave a comment here with your real name
• PR's commit messages follow the commit message format

If you need to make changes to your pull request, you can update the commit with git commit --amend.
Then, update the pull request with git push -f.

Thanks again for your help!

[bsiddiqui]

signed CLA, not sure why this doesn't meet message format

[petebacondarwin]

@bsiddiqui - Thanks for the PR. Did you read our commit message format guidelines?
Your commit message should look like:

docs($anchorScroll): use correct controller in example

By the way, this is a duplicate of #3898. So closing for now.