title: Formik FieldArray not rerendering on updated values even with enableReinitialize
body: <p><a href="https://jaredpalmer.com/formik/docs/api/formik#enablereinitialize-boolean" rel="nofollow noreferrer">Formik enableReinitialize documentation</a></p>
  
  <blockquote>
    <p>Default is false. Control whether Formik should reset the form if initialValues changes (using deep equality).</p>
  </blockquote>
  
  <p>I'm passing in an object (through props) that I set in 
  initialValues, the object definition is:</p>
  
  <pre><code>{
    "shoppingList": {
      "title": "",
      "items": [ { "quantity": 0, description: "" } ]
    }
  }
  </code></pre>
  
  <p>I'm using this in a Formik FieldArray component. I'm updating the quantity in a button onClick handler using an inline arrow function that <strong>directly mutates</strong> the item via current element param in <code>items.#map</code> callback.</p>
  
  <p>Formik is not rerendering the form to reflect the updated quantity. Formik knows about the quantity as when I submit the form the component storing quantity is rerendered to the correct updated quantity.</p>