Flow RecordOf<T> ignores T type 

Flow: 0.84.0
Immutable: 4.0.0-rc.11

The following code doesn't produce an error.
```
// @flow
import { Record } from 'immutable';
import type { RecordOf, RecordFactory } from 'immutable';

type Foo = {| foo: string |};

const fooFactory: RecordFactory<Foo> = Record({ foo: 1, bar: 2 });
const foo: RecordOf<Foo> = fooFactory();
```