There was a problem with the one-line docker install here: https://dgraph.io/docs/get-started/
After re-installing using docker pull it worked.
I have installed dgraph on a DigitalOcean Docker Droplet. Installing and using docker run doesn’t provide unix with a command line dgraph command. So I cannot do any configuration. It says:
Command 'dgraph' not found, but can be installed with: snap install dgraph
How can I now alter my settings? For example: protect access with a password / API key 
Thanks,
Klaas