Small grammatical cleanup in client-credentials-setup.md

[dannyscript]

Description

Small grammatical cleanup in the "Setup with Client Credentials Grant" guide

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own changes
• [x] I have run yarn lint to make sure my changes pass all linters
• [x] I have pulled the latest changes from the upstream developer branch

[CLAassistant]

All committers have signed the CLA.