Issue:
When exporting an opaque Flow type and importing it into an entry file for documentation to consume, the CLI throws an error when using the readme command.

Example:

// MyType.js
export opaque type MyType: string = string

// index.js
import type { MyType } from './MyType'

> yarn documentation README ./index.js --document-exported

Error: Unable to find the value MyType in /Users/andrewdelprete/path/to/MyType.js

• What version of documentation.js are you using?: v13.0.0

• How are you running documentation.js (on the CLI, Node.js API, Grunt, other?): CLI