Typescript: useFieldArray second argument (config) should be optional

[Yankovsky]

export function useFieldArray<
  FieldValue = any,
  T extends HTMLElement = HTMLElement
>(
  name: string,
  config: UseFieldArrayConfig<FieldValue>
): FieldArrayRenderProps<FieldValue, T>

config should be optional, right? Just like in react-final-form. Readme clearly states

The useFieldArray hook takes two parameters, the first is the name of the field, and the second is an optional object that looks just like FieldArrayProps, except without the name. It returns an object just like FieldArrayRenderProps.

I'll make a pr.

[erikras]

Published fix in v3.1.1.