It's not your problem, it's their problem. A valid SSL (Secure Socket Layer) certificate from a trust CA (Certifying Authority) is required to communicate over HTTPS. These certificates have an expiration date and once that's past, any communication attempts over HTTPS will yield that error.
Most browsers redirect HTTP traffic over HTTPS, and if the SSL certificate has expired, HTTPS cannot be trusted to be secure and as such the browsers don't proceed any further and that's a good thing.
If you know the contact info for the website folks, then send them a note to let them know to renew their SSL certificate.
You can check this certificate on any website utilized HTTPS by clicking on the padlock icon in the URL bar (most browsers have it) checking the certificate expiration date.
