Bug is caused by socket.io's ssl certificate expiring
To paraphrase Chris Brown, these CDNs ain’t loyal. If you used Socket.IO for your web app, you may have run into a few issues today, 5/27/16. A few issues is probably a bit of an understatement, as any secure app that used Socket.IO’s CDN to serve their client the necessary library to communicate with their server today was crippled.
It was a simple fix to get ... back up and running (I just downloaded a copy of the socket.io.js file, hosted it locally, and changed the reference to the file in my app accordingly),