Update 2018-10-23-grpc-web-ga.md

[addie]

Fix spelling

[thelinuxfoundation]

Thank you for your pull request. Before we can look at your contribution, we need to ensure all contributors are covered by a Contributor License Agreement.

After the following items are addressed, please respond with a new comment here, and the automated system will re-verify.

• User @addie isn't covered by a CLA. They will need to complete the form at https://identity.linuxfoundation.org/projects/cncf

Regards,
CLA GitHub bot

[carl-mastrangelo]

LGTM, but sadly we still need CLA bot to approve.

[thisisnotapril]

@addie can you please review the CLA for this PR? Thank you!