title: Formik onChange Handler not firing when child component is a hook
body: <p>Making a form with react + formik and wanting to use hooks to handle the child components state. When I <em>hook</em> up (haha) my hookified component to my form,  the formik onChange handler does not fire as expected.</p>
  
  <p>Form Code</p>
  
  <pre><code>... snip ...
    const classes = useStyles()
    return (
      &lt;div&gt;
        &lt;FieldArray
          name='sessions'
          render={arrayHelpers =&gt; (
            &lt;div&gt;
              {values.sessions.map((data, i) =&gt; {
                return (
                  &lt;div className={classes.formControl} key={i}&gt;
                    &lt;TextField
                      margin='dense'
                      variant='outlined'
                      error={shouldShowError(
                        errors,
                        touched,
                        `sessions.${i}.name`
                      )}
                      style={{ display: 'flex', flex: 1 }}
                      value={values.sessions[i].name}
                      label={I18n.t('sessions.name.label')}
                      name={`sessions.${i}.name`}
                      onChange={handleChange}
                      onBlur={() =&gt; setFieldTouched(`sessions.${i}.name`)}
                    /&gt;
                    &lt;DaysofWeek
                      value={values.sessions[i].days}
                      label={I18n.t('sessions.days.label')}
                      name={`sessions.${i}.days`}
                      onChange={handleChange}
                    /&gt;
  ... snip ...
  </code></pre>
  
  <p>When I replace the <code>onChange</code> line in DaysOfWeek with <code>{data =&gt;console.log(data)}</code> I see the data I expect in the console.</p>
  
  <p>I should also note that the TextField component in this form updates formik correctly.</p>
  
  <p>For reference, heres the DaysOfWeek component code:</p>
  
  <pre><code>import React from 'react'
  import { makeStyles } from '@material-ui/core/styles'
  import FormControl from '@material-ui/core/FormControl'
  import FormGroup from '@material-ui/core/FormGroup'
  import FormControlLabel from '@material-ui/core/FormControlLabel'
  import FormLabel from '@material-ui/core/FormLabel'
  import Checkbox from '@material-ui/core/Checkbox'
  import { symmetricDifference } from 'ramda'
  
  const useStyles = makeStyles(theme =&gt; ({
    root: {
      display: 'flex'
    },
    formControl: {
      margin: theme.spacing(0)
    }
  }))
  
  export default function DaysofWeek ({ days = [], label = '', onChange }) {
    const classes = useStyles()
    const [stateDays, setState] = React.useState(days)
  
    const handleChange = value =&gt; _event =&gt; {
      let updatedDays = symmetricDifference([value], stateDays).sort()
      setState(updatedDays)
      onChange(updatedDays)
    }
  
    const staticDays = [
      [ 0, 'Sun' ],
      [ 1, 'Mon' ],
      [ 2, 'Tue' ],
      [ 3, 'Wed' ],
      [ 4, 'Thu' ],
      [ 5, 'Fri' ],
      [ 6, 'Sat' ]
    ]
  
    return (
      &lt;div className={classes.root}&gt;
        &lt;FormControl component='fieldset' className={classes.formControl} &gt;
          &lt;FormLabel component="legend"&gt;{label}&lt;/FormLabel&gt;
         { staticDays.map(([dayNum, dayLabel]) =&gt; 
          &lt;FormGroup key={dayNum}&gt;
            &lt;FormControlLabel
              control={
                &lt;Checkbox checked={stateDays.includes(dayNum)} onChange={handleChange(dayNum)} /&gt;
              }
              label={dayLabel}
            /&gt;
          &lt;/FormGroup&gt;
         )}
        &lt;/FormControl&gt;
      &lt;/div&gt;
    )
  }
  </code></pre>
  
  <p>Relevant bits of package.json:</p>
  
  <pre><code>    "@material-ui/core": "^4.3",
      "@material-ui/icons": "^4.2",
      "@material-ui/pickers": "^3.2.4",
      "classnames": "^2.2.6",
      "date-fns": "^2.0.1",
      ....
      "formik": "2.0.1-rc.13",
       ....
      "react": "^16.8.6",
      "react-apollo": "^2.5.5",
      "react-dom": "^16.8.6",
      "react-icons": "^3.6.1",
  .....
  </code></pre>
  
  <p>How do I get the onChange from formik to update my formik state?</p>