Update reference.html - getTotalMarkers()

[thisisthefuture]

Description of getTotalMarkers() is incorrect. The comment for getTotalMarkers() and in use shows the method returns the number of markers in the clusterer, not an array.

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

:memo: Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[thisisthefuture]

I signed it!

[googlebot]

CLAs look good, thanks!

[Remo]

@thisisthefuture unfortunately google doesn't support this repo anymore, but we've merged your changes to our own fork https://github.com/gmaps-marker-clusterer/gmaps-marker-clusterer documentation can be found here https://gmaps-marker-clusterer.github.io/gmaps-marker-clusterer/#methods