I found that I can upgrade Discourse from /admin/docker (message: New Version Available!), despite the fact that I used the latest version (0.9.9.15). Of course I clicked “Upgrade” and process stopped at “$ bundle exec rake assets:precompile discourse”.
Now I still have a message “Currently Upgrading…”. I tried to click “Reset Upgrade”, restart server (Digital Ocean) and rebuild app (./launcher rebuild app), but nothing helped. I still have this message. Should I do something about it? Is it important?