Issue description

Our docker builds failed this morning due to a change in behaviour when running pipenv install in the root directory.
When running with the latest version (2020.5.28) an error is thrown after dependencies are built and installed ERROR: Pipenv is not intended to work under the root directory, please choose another path.
It looks like this is a change introduced in #3386, relating to an issue raised in #3434.
This issue is really just to point out that this behaviour change should be listed as breaking in the changelog, as it doesn't currently appear to be mentioned.
For the time being we have worked around this by pinning pipenv to the last version (2018.11.26).

Expected result

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Actual result

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Steps to replicate

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