Update Dockerfile (revert back to last working version)

1 job for master in 18 minutes and 47 seconds (queued for 2 seconds)
Name Stage Failure
image_build Build
  Rate limit reset at: 2021-08-27 13:29:30 UTC

To increase your GitHub API rate limit
- Use `usethis::browse_github_pat()` to create a Personal Access Token.
- Use `usethis::edit_r_environ()` and add the token as `GITHUB_PAT`.
Execution halted
The command '/bin/sh -c R -f /tmp/install.R && pip3 install -r /tmp/requirements.txt' returned a non-zero code: 1
Cleaning up file based variables
ERROR: Job failed: exit code 1