Fix python-3.6 CircleCI tests

[xhluca]

Seems like it's currently failing:

#!/bin/bash -eo pipefail
. venv/bin/activate
pip install -r tests/requirements.txt --quiet

pytest-cookies 0.5.1 has requirement pytest<6.0.0,>=3.3.0, but you'll have pytest 6.2.2 which is incompatible.
Command "/home/circleci/project/venv/bin/python -u -c "import setuptools, tokenize;__file__='/tmp/pip-install-7nfc7x4u/cryptography/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-record-fhb8jvs6/install-record.txt --single-version-externally-managed --compile --install-headers /home/circleci/project/venv/include/site/python3.6/cryptography" failed with error code 1 in /tmp/pip-install-7nfc7x4u/cryptography/
You are using pip version 18.1, however version 21.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

Exited with code exit status 1
CircleCI received exit code 1

[alexcjohnson]

hackebrot/pytest-cookies#53 - we could install from that branch, or fork the project if we conclude it has been abandoned.

[xhluca]

Is pytest-cookies 0.5.1 actually causing the test to fail, or is it cryptography? Feel like the former is just a warning but it might cause it to fail (in which case i'd agree with making a fork and perhaps release it as pytest-cookies-plotly)? If it's not used anywhere else in the plotly org I guess it doesn't hurt to pin it to the commit

[alexcjohnson]

Ah you may be right - I didn't notice that the long line there ended in the cryptography error. So yeah, the same fix we did elsewhere will probably solve it.