Fixed typo in docs

[AlexeyNikipelau]

To see the logs from the Cloud Build CI, please join either our discussion or announcement mailing list.

---

This change is 

[google-cla[bot]]

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).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[rthadur]

@AlexeyNikipelau please sign cla https://github.com/tensorflow/tfjs/pull/6494/checks?check_run_id=6803868850

[jenperson]

This PR is being closed because the typo has since been fixed.