Update pip to 20.2.2

[pyup-bot]

This PR updates pip from 20.2.1 to 20.2.2.

Changelog

20.2.2

===================

Bug Fixes
---------

- Only attempt to use the keyring once and if it fails, don't try again.
This prevents spamming users with several keyring unlock prompts when they
cannot unlock or don't want to do so. (`8090 <https://github.com/pypa/pip/issues/8090>`_)
- Fix regression that distributions in system site-packages are not correctly
found when a virtual environment is configured with ``system-site-packages``
on. (`8695 <https://github.com/pypa/pip/issues/8695>`_)
- Disable caching for range requests, which causes corrupted wheels
when pip tries to obtain metadata using the feature ``fast-deps``. (`8701 <https://github.com/pypa/pip/issues/8701>`_, `8716 <https://github.com/pypa/pip/issues/8716>`_)
- Always use UTF-8 to read ``pyvenv.cfg`` to match the built-in ``venv``. (`8717 <https://github.com/pypa/pip/issues/8717>`_)
- 2020 Resolver: Correctly handle marker evaluation in constraints and exclude
them if their markers do not match the current environment. (`8724 <https://github.com/pypa/pip/issues/8724>`_)

Links

• PyPI: https://pypi.org/project/pip
• Changelog: https://pyup.io/changelogs/pip/
• Homepage: https://pip.pypa.io/

[duckinator]

bors r+

[bors]

Build succeeded:

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• FreeBSD LANG:C.UTF-8 LC_ALL:C.UTF-8 PYTHON:3.8
• FreeBSD LANG:en_US.UTF-8 LC_ALL:en_US.UTF-8 PYTHON:3.6
• Lint
• Linux container:python:3.6-slim
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• Linux_Py35
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• Windows container:python:3.6-windowsservercore-1809
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