Missing `watch` permission in rbac for agones-sdk

Getting the following error in the logs.
`{"level":"error","msg":"agones.dev/agones/pkg/client/informers/externalversions/factory.go:74: Failed to watch *v1alpha1.GameServer: unknown (get gameservers.stable.agones.dev)","time":"2018-07-19T21:52:23Z"}`

Needed the `watch` permission to make it go away.

We aren't watching for events right now, so it's just noise,
but it's better with it gone.