Update pip Version for cimg/python:3.7.7

[danhlee329]

When running pipenv run safety check --full-report with base image cimg/python:3.7.7 in a CircleCI job, getting security finding below:

#!/bin/bash -eo pipefail
pipenv run safety check --full-report

safety report
checked 39 packages, using free DB (updated once a month)
---
-> pip, installed 20.1.1, affected <21.1, id 40291
Pip 21.1 stops splitting on unicode separators in git references, which could be maliciously used to install a different revision on the repository. See: <https://github.com/pypa/pip/issues/9827>. Additionally, pip 21.1 updates urllib3 to 1.26.4 to fix CVE-2021-28363.
--

Exited with code exit status 255
CircleCI received exit code 255

Able to workaround this by running command pipenv run pip3 install --upgrade pip, but would like to see if pip can be upgraded.

[FelicianoTech]

We wouldn't update the image. So either you need to update it yourself, as mentioned, or use a newer Python image which would contain a newer pip version.