pubsub: mark GAX_CONFIG as private
pubsub: mark GAX_CONFIG as private

GoogleCloudPlatform/gcloud-node,jgeewax/gcloud-node,jgeewax/gcloud-node,callmehiphop/gcloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,GoogleCloudPlatform/gcloud-node,GoogleCloudPlatform/gcloud-node,callmehiphop/gcloud-node,googleapis/google-cloud-node