Update dependency google-auth to v1.18.0

[renovate-bot]

This PR contains the following updates:

Package	Update	Change
google-auth	minor	==1.17.2 -> ==1.18.0

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Release Notes

googleapis/google-auth-library-python

v1.18.0

Compare Source

Features

• make load_credentials_from_file a public method (#​530) (15d5fa9)

Bug Fixes

• no warning if quota_project_id is given (#​537) (f30b45a)

1.17.2 (2020-06-12)

Bug Fixes

• dependencies: Further restrict RSA versions (#​532) (46677a0), closes #​528

1.17.1 (2020-06-11)

Bug Fixes

• narrow acceptable RSA versions to maintain Python 2 compatability (#​528) (9434868)

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