How to properly reference flow-typed in custom type declarations?

Let's say I use `bunyan` npm package and there is `flow-typed` for it already (https://github.com/flowtype/flow-typed/blob/master/definitions/npm/bunyan_v1.x.x/flow_v0.21.x-/bunyan_v1.x.x.js).

What I'm trying to achieve now is this:

```
declare class Context {
userId: string;
logger: bunyan.Logger;
};
```

And `flow` is failing with the following error:

```
type-annotation `bunyan`. Could not resolve name
```

I'm not quite sure what's going on and how to make it happy. Thanks!