How to fix curl: (60) SSL certificate: Invalid certificate chain
Using the Safari browser (not Chrome, Firefox or Opera) on Mac OS X 10.9 (Mavericks) visit https://registry.npmjs.org
Click the Show certificate button and then check the checkbox labelled Always trust. Then click Continue and enter your password if required.
Curl should now work with that URL correctly.
The problem is an expired intermediate certificate that is no longer used and must be deleted. Here is a blog post from Digicert explaining the issue and how to resolve it.
https://blog.digicert.com/expired-intermediate-certificate/
I was seeing the issue with Github not loading via SSL in both Safari and the command line with git pull. Once I deleted the old expired cert everything was fine.