Passing version=None to discovery.build(), with intent to always
get the latest version of the discovery document,
no longer attempts to use Discovery V1, which fails with
Bad Request errors.
Instead, it uses Discovery V2, which supports null version use case.

Fixes: #971

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Fixes #995  🦕

fixed link based on https://developers.google.com/identity/protocols/oauth2/service-account

* chore: updated CHANGELOG.md [ci skip]

* chore: updated setup.cfg [ci skip]

* chore: updated setup.py

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>