Upgrade dependency versions. (#331)
Upgrade dependency versions. (#331)

* Upgrade Fluentd to 1.6.3.
* Upgrade googleapis-common-protos to 1.3.9.
* Upgrade googleauth to 0.9.0.
* Upgrade google-api-client to 0.30.8.
* Upgrade google-cloud-logging to 1.6.6.
* Upgrade json to 2.2.0.

GoogleCloudPlatform/fluent-plugin-google-cloud