Address TF Serving GRPC Warning

[deliahu]

Description

cx logs on an API:

/usr/local/lib/python3.5/dist-packages/tensorflow_serving/apis/prediction_service_pb2.py:131: DeprecationWarning: beta_create_PredictionService_stub() method is deprecated. This method will be removed in near future versions of TF Serving. Please switch to GA gRPC API in prediction_service_pb2_grpc.
  'prediction_service_pb2_grpc.', DeprecationWarning)