Fix broken Dockerfile (fixes #52)

[globau]

Fix broken Dockerfile

Checklist

Not all of these might apply to your change but the more you are able to check the easier it will be to get your contribution merged.

• [ ] CI passes
• [ ] Description of proposed change
• [ ] Documentation (README, docs/, man pages) is updated
• [X] Existing issue is referenced if there is one
• [ ] Unit tests for the proposed change

[globau]

Looks like all of the other open PRs are attempts to fix this issue. Closing.