Anyone with an app affected by this because you use Heroku's SSL endpoint can fix this by switching to SNI. Unfortunately Heroku's API is also affected. There is a workaround... just edit your hosts file to point to the proper ip addresses temporarily.

add to /etc/hosts

23.21.149.112 api.heroku.com 107.21.99.123 ssl-doctor.heroku.com

Then use Heroku CLI to switch your app to the new SNI endpoint

heroku certs:add --type sni server.crt server.key -a YOUR_APP

That will spit out a new host name that you can point your DNS to and still be online.