title: Formik + Yup don't validate input if untouched
body: <p>I am trying to use Formik + Yup to validate my form, but currently if I touch one field, and then try and submit, a field that has a minimum length will validate, and not allow me to submit. </p>
  
  <p>Following my code sandbox (<a href="https://codesandbox.io/s/focused-bardeen-5fiuz" rel="nofollow noreferrer">https://codesandbox.io/s/focused-bardeen-5fiuz</a>), I want the user to be able to submit the form if they just change the <code>firstName</code> field, but without entering anything for the <code>country</code> field. I tried both the <code>.notRequired()</code> and <code>.nullable(true)</code> params, but did not work. Any idea how to achieve this?</p>