Hey guys. I ran into the same problem. Thank you to Vlad for the solution. However, I feel like it needs some explanation. What worked for me was sending the command from the homeassistant docker image cmdline. If you have SSH access or console access to your raspberry pi (or docker host), you can get to the shell of the homeassistant image. You use:
docker exec -it homeassistant /bin/bash
then issue:
curl -d '{"version": "0.60"}' http://hassio/homeassistant/update
Takes about 10 minutes as mentioned by Vlad