gRPC leak

[callmehiphop]

Possibly relates to #1140

I received this error locally running Node v0.12.7.

1) PubSub subscribe should create a Topic object from a string:
   Uncaught Error: .google.pubsub.v1.Subscription#a is not a field: undefined
      at Error (native)
      at MessagePrototype.set (node_modules/grpc/node_modules/protobufjs/dist/ProtoBuf.js:2440:58)
      at MessagePrototype.set (node_modules/grpc/node_modules/protobufjs/dist/ProtoBuf.js:2434:38)
      at Message (node_modules/grpc/node_modules/protobufjs/dist/ProtoBuf.js:2363:34)
      at serialize (node_modules/grpc/src/node/src/common.js:76:23)
      at Client.makeUnaryRequest [as createSubscription] (node_modules/grpc/src/node/src/client.js:303:19)
      at PubSub.GrpcService.request (lib/common/grpc-service.js:214:28)
      at lib/common/grpc-service.js:187:12
      at lib/common/grpc-service.js:285:5
      at addScope (node_modules/google-auto-auth/index.js:74:5)
      at callback (node_modules/google-auto-auth/node_modules/google-auth-library/lib/auth/googleauth.js:41:5)
      at node_modules/google-auto-auth/node_modules/google-auth-library/lib/auth/googleauth.js:124:9