Update virtualenv requirement from ~=20.4 to ~=20.6 (#59)
Update virtualenv requirement from ~=20.4 to ~=20.6 (#59)

Updates the requirements on [virtualenv](https://github.com/pypa/virtualenv) to permit the latest version.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](https://github.com/pypa/virtualenv/compare/20.4.0...20.6.0)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
kyhau/reko