Fix issue with pip 20.0 breaking on install (#6598)
Fix issue with pip 20.0 breaking on install (#6598)

* Upgrade pip to above its broken version

* Call virtualenv without no-download

* Add comment

* link to issue: https://github.com/readthedocs/readthedocs.org/issues/6585

rtfd/readthedocs.org,rtfd/readthedocs.org,rtfd/readthedocs.org,rtfd/readthedocs.org