Change path to file seed.dat

[jviki]

When deploying a docker container via docker compose or swarm, the secrets should be passed via the secrets interface. Such secrets are mounted at /run/secrets/<name>. It should be possible to load such secrets file directly. Currently, it seems that the only possible way is to customize the current Dockerfile to add some shell magic like cat /run/secrets/seed and pass the seed via command line which is very insecure or to do make a symlink to the secrets file.

https://docs.docker.com/compose/how-tos/use-secrets/