chore: set release version to 2.0.0 (#840)
chore: set release version to 2.0.0 (#840)

* chore: release 2.0.0

* Update CHANGELOG.md

* chore: set version number to 2.0.0

Follow up to #829

Co-authored-by: release-please[bot] <6fb7beb84df8ef60a675db3372864553c0b582c5@users.noreply.github.com>
googleapis/google-auth-library-python,googleapis/google-auth-library-python