Are you submitting a bug report or a feature request?

Bug report

What is the current behavior?

If required prop is initially true, then the validate function continues to require the field to be filled in, even if you later change the required prop to false.

What is the expected behavior?

As soon as required prop changes, validation checks should reflect that that. So if you change it to false, the field should no longer be required.

Sandbox Link

https://codesandbox.io/s/react-final-form-html5-validation-example-n2q8d

Other information

Likely related to #13