Bump virtualenv from 20.4.6 to 20.6.0

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Bumps virtualenv from 20.4.6 to 20.6.0.

Changelog

Sourced from virtualenv's changelog.

v20.6.0 (2021-07-14)

Features - 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) <https://github.com/pypa/virtualenv/issues/1910>`_)
v20.5.0 (2021-07-13)
Features - 20.5.0

• Plugins now use 'selectable' entry points - by :user:jaraco. ([#2093](https://github.com/pypa/virtualenv/issues/2093) <https://github.com/pypa/virtualenv/issues/2093>_)
• add libffi-7.dll to the hard-coded list of dlls for PyPy ([#2141](https://github.com/pypa/virtualenv/issues/2141) <https://github.com/pypa/virtualenv/issues/2141>_)
• Use the better maintained platformdirs instead of appdirs - by :user:gaborbernat. ([#2142](https://github.com/pypa/virtualenv/issues/2142) <https://github.com/pypa/virtualenv/issues/2142>_)

Bugfixes - 20.5.0

- Bump pip the embedded pip ``21.1.3`` and setuptools to ``57.1.0`` - by :user:`gaborbernat`. (`[#2135](https://github.com/pypa/virtualenv/issues/2135) <https://github.com/pypa/virtualenv/issues/2135>`_)
Deprecations and Removals - 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) <https://github.com/pypa/virtualenv/issues/2141>_)

v20.4.7 (2021-05-24)

Bugfixes - 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) <https://github.com/pypa/virtualenv/issues/2123>`_)

Commits

• 75f0202 release 20.6.0
• c52fe3e Support without distutils (#2146)
• 0705f20 Merge pull request #2145 from pypa/release-20.5.0
• ca0d409 release 20.5.0
• f66d0a8 Use platformdirs instead of appdirs (#2142)
• ce6efc8 Drop Python 3.4 support (#2143)
• c746322 [pre-commit.ci] pre-commit autoupdate (#2144)
• 63e884e add libffi-7.dll to pypy on windows (#2141)
• 17caadc Rely on 'selectable' interface for entry points. (#2126)
• 03afeca Bump embeded pip (#2135)
• Additional commits viewable in compare view

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