Bump virtualenv from 20.2.2 to 20.3.0 in /requirements

[dependabot]

Bumps virtualenv from 20.2.2 to 20.3.0.

Changelog

Sourced from virtualenv's changelog.

v20.3.0 (2021-01-10)

Features - 20.3.0

- The builtin discovery takes now a ``--try-first-with`` argument and is first attempted as valid interpreters. One can
  use this to force discovery of a given python executable when the discovery order/mechanism raises errors -
  by :user:`gaborbernat`. (`[#2046](https://github.com/pypa/virtualenv/issues/2046) <https://github.com/pypa/virtualenv/issues/2046>`_)
Bugfixes - 20.3.0

• On Windows python 3.7+ distributions where the exe shim is missing fallback to the old ways - by :user:gaborbernat. ([#1986](https://github.com/pypa/virtualenv/issues/1986) <https://github.com/pypa/virtualenv/issues/1986>_)
• When discovering interpreters on Windows, via the PEP-514, prefer PythonCore releases over other ones. virtualenv is used via pip mostly by this distribution, so prefer it over other such as conda - by :user:gaborbernat. ([#2046](https://github.com/pypa/virtualenv/issues/2046) <https://github.com/pypa/virtualenv/issues/2046>_)

Commits

• a4025d6 release 20.3.0
• 684a632 Improve discovery on Windows and provide escape hatchet (#2046)
• 9201a75 [pre-commit.ci] pre-commit autoupdate (#2045)
• 36fba76 Remove xdist (#2043)
• bc787b2 Try to fix the CI (#2041)
• 838bfbc [pre-commit.ci] pre-commit autoupdate (#2042)
• 1b8144f Checkout entire branch, not just last commit
• 287629a Add 3.9 to doc list of cpython versions (#2033)
• 8b8a249 Merge pull request #2030 from pypa/release-20.2.2
• See full diff in compare view

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[dependabot]

Superseded by #501.