You are getting the warning because the credentials they use use to encrypt traffic is expired, which in and of itself doesn't really have any repercussions. They expire to reduce the time an entity has to brute force an key, and to minimize the time that revoked credentials could be used on a device that hasn't checked for updates. Neither of those are likely to be a problem here, especially since it's a static web page that doesn't collect any user data, so the worst case scenario is that if there were no security, a man-in-the-middle could tell which links you clicked on, but nothing more.