Add periods to list in upgrading-your-accounts-plan#troubleshooting-a-500-error-when-upgrading

[nguyenalex836]

Code of Conduct

• I have read and agree to the GitHub Docs project's Code of Conduct

What article on docs.github.com is affected?

https://docs.github.com/en/billing/managing-the-plan-for-your-github-account/upgrading-your-accounts-plan#troubleshooting-a-500-error-when-upgrading

What part(s) of the article would you like to see updated?

If you receive a 500 error when trying to upgrade your account:

• Try clearing your browser's cache, then resubmit your information
• Check to make sure you have entered your payment data correctly

Add periods to the end of each list line, as each line is a complete sentence

Additional information

Style guide reference