More detailed error msg when not able to connect to MailChimp API endpoint

Hey,

I had this error with Mailchimp: Unable to connect to the MailChimp API endpoint.

Then I googled it but I found (almost) nothing. With this patch I get: Unable to connect to the MailChimp API endpoint because Hostname/IP doesn't match certificate's altnames

...which points me to thousands of websites about how to solve TLS problems with node ;)

Cheers, Philip