I am trying to install a local Docker image of CoCalc, however, I'd like to keep using Sage-8.9 with Python2. Following the github instructions, I run
docker run --name=cocalc -d -v ~/cocalc:/projects -p 443:443 sagemathinc/cocalc
which results in Sage-9.1, so all my code stops working. How do I switch to Sage-8.9 with docker?