I checked my pip3 & python3 version:
(tensorflow) MacBook-Pro-de-Hector-2:tensorflow hectoresteban$ pip3 -V pip 10.0.1 from /Users/hectoresteban/.
I tried this command on macOS Catalina (Python 3.6) and it ran properly:
$ python3 -m pip install --upgrade https://storage.googleapis.com/tensorflow/mac/cpu/tensorflow-1.12.0-py3-none-any.whl