Re-export AsyncValidationError in the build result

[imballinst]

Hello, thank you for creating this library!

I wonder if we can re-export AsyncValidationError in this line?

async-validator/src/index.ts

Lines 1 to 8 in b9a84a7

	import {
	format,
	complementError,
	asyncMap,
	warning,
	deepMerge,
	convertFieldsError,
	} from './util';

Something like this:

export { AsyncValidationError } from './util'

This is so that, if we use it with async/await, we can do something like this, similar like what we usually do with axios and AxiosError:

import { AsyncValidationError } from 'async-validator'

try {
  await schema.validate(...)
} catch (err) {
  if (err instanceof AsyncValidationError) {
    // Do stuff...
  }
}

I can open a PR if it's possible, let me know what you think. Thanks!