v0.1.3: Making `google-cloud-pubsub==0.30.1` release. (#4644)

Notable Implementation Changes

• Apply scopes to explicitly provided credentials if needed (#4594).
• Removing google.api_core.gapic_v1.method.METRICS_METADATA_KEY. It
  can be accessed via
  google.api_core.gapic_v1.client_info.METRICS_METADATA_KEY (#4588).

Dependencies

• Upgrading to latest grpcio==1.8.2 (#4642). For details, see
  related gRPC bug
  and fix.

PyPI: https://pypi.org/project/google-api-core/0.1.3/