datastore: force older version of grpc (#2261, #2268)
datastore: force older version of grpc (#2261, #2268)

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