How do I fix the SSL warning I get when visiting github.com?

I see the following warning when visiting http://www.github.com/ after July 26, 2014. I get this warning in both Chrome and Safari on my OS X Mavericks-equipped iMac.

Should I worry about this? How do I fix it?

Should I worry about this?

You should always distrust SSL connections that are using expired certificates. This could indicate a simple oversight on the part of the website operator or it could indicate a malicious attempt to intercept encrypted communications between the website and your browser. Heed your browser's warnings and don't load the page when these warnings occur.

How do I fix it?

OS X users can delete the expired certification from their keychains. This certificate was issued by DigiCert and they have a blog post that details what happened and how to fix it. Paraphrased from the post:

1. Start the Keychain Access application (you may be asked for your password when you do this)
2. In Keychain Access go to View -> Show Expired Certs and search for DigiCert High to find the DigiCert High Assurance EV Root CA that expired on July 26, 2014. It's important you only delete the expired certificate here.
3. Delete this certificate and close Keychain Access.

You may also need to restart Chrome and Safari for the warning to disappear. Also, make sure you check all Keychains and verify your Category filters - certificates or All Items should be selected.