Update google-cloud-logging requirement from ~=1.14 to ~=1.15
Update google-cloud-logging requirement from ~=1.14 to ~=1.15

Updates the requirements on [google-cloud-logging](https://github.com/googleapis/python-logging) to permit the latest version.
- [Release notes](https://github.com/googleapis/python-logging/releases)
- [Changelog](https://github.com/googleapis/python-logging/blob/master/CHANGELOG.md)
- [Commits](https://github.com/googleapis/python-logging/compare/v1.14.0...v1.15.1)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
snarfed/oauth-dropins,snarfed/oauth-dropins,snarfed/oauth-dropins