Components that are cast (Flow) on export deemed invalid

It looks like if you cast a component on export, ex: `export default (MyComponent: React.ComponentType<X>)`, the `react-docgen` does not feel that it's a valid component.

I think I can create a fix for this, but I'm not sure how to get the `value` definition of an `Identifier` in the AST. Any help would be appreciated.