Service 'app' failed to build

[niwashun]

$ docker-compose up

...

## Confirming "focal" is supported...

+ curl -sLf -o /dev/null 'https://deb.nodesource.com/node_6.x/dists/focal/Release'

## Your distribution, identified as "focal", is not currently supported, please contact NodeSource at https://github.com/nodesource/distributions/issues if you think this is incorrect or would like your distribution to be considered for support

ERROR: Service 'app' failed to build: The command '/bin/sh -c curl -sL https://deb.nodesource.com/setup_6.x | bash - && apt-get install -y nodejs' returned a non-zero code: 1

"ubuntu:latest" in the base image of Dockerfile-app is now Ubuntu 20.04 LTS "Focal Fossa", so Node.js 6.x is not supported.