I noticed that you said you "don't understand the error" yet you wanted to bypass it. This line of thinking is exactly the problem. I don't mean that in a condescending way. Disabling the last line of defense as a matter of routine is resulting in more and more attacks, so Google wants to move the problem to where it should be - the misconfigured website.
The short version is that during a previous visit to that site, it sent an HSTS HTTP header, which is really the only protection there is against SSL stripping attacks. Basically, it tells your browser, "My site will ALWAYS be SSL (and valid SSL) - if I ever tell you otherwise, it's not me, so do not communicate."
HSTS is relatively new, so browsers are handling it a bit differently and you don't see it often. A broken SSL chain on a site that did not give you HSTS would still allow you to ignore it.
Is it typical for front-enders in Rails to not know web security / SSL?
Do we really need to be sniping?
The site's security certificate is not trusted! You attempted to reach www.jottit.com, but the server presented a certificate issued by an entity that is not trusted by your computer's operating system. This may mean that the server has generated its own security credentials, which Google Chrome cannot rely on for identity information, or an attacker may be trying to intercept your communications. You cannot proceed because the website operator has requested heightened security for this domain.