When running:
tutor dev run -m /path/to/edx-platform lms
pip install -r requirements/edx/development.txt
I realised that I was re-installing packages that should already have been
present in the image. The reason for that was that I was running an outdated
version of the dev version of the openedx Docker image. This happens because
`tutor dev run` does not trigger an image re-build.
We solve this issue by pinning the openedx dev Docker image tag to the current
tutor version.
