Downgrade gRPC to ~1.7 (#2784)
Downgrade gRPC to ~1.7 (#2784)

https://github.com/grpc/grpc-node/issues/130
https://github.com/googleapis/nodejs-datastore/issues/35
GoogleCloudPlatform/gcloud-node,jgeewax/gcloud-node,GoogleCloudPlatform/gcloud-node,jgeewax/gcloud-node,googleapis/google-cloud-node,GoogleCloudPlatform/gcloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node