Update virtualenv to 20.6.0

[pyup-bot]

This PR updates virtualenv from 20.4.6 to 20.6.0.

Changelog

20.6.0

~~~~~~~~~~~~~~~~~
- Support Python interpreters without ``distutils`` (fallback to ``syconfig`` in these cases) - by :user:`gaborbernat`. (`1910 <https://github.com/pypa/virtualenv/issues/1910>`_)

20.5.0

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Drop python ``3.4`` support as it has been over 2 years since EOL - by :user:`gaborbernat`. (`2141 <https://github.com/pypa/virtualenv/issues/2141>`_)

20.4.7

~~~~~~~~~~~~~~~~~
- Upgrade embedded pip to ``21.1.2`` and setuptools to ``57.0.0`` - by :user:`gaborbernat`. (`2123 <https://github.com/pypa/virtualenv/issues/2123>`_)

Links

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

[pyup-bot]

Closing this in favor of #1646