Follow up and update firebase-admin once hoek dependancies updated to >= 5.0.3

`hoek` versions < 5.0.3 have a potential Prototype pollution vulnerability. `firebase-admin` is our base dependency that eventually includes `hoek`.

firebase-admin: https://github.com/firebase/firebase-admin-node/issues/217
~grpc-node:~ ~https://github.com/grpc/grpc-node/issues/225~ ~https://github.com/grpc/grpc-node/pull/311~
~node-pre-gyp: https://github.com/mapbox/node-pre-gyp/issues/356~