title: Checkbox onChange event is not handled by handleChange props by Formik
body: <p>I was building simple Form using <code>React</code> and <code>Formik</code> library.
  I have added check box inside the <code>form</code> tag which is wrapped by <code>withFormik</code> wrapper of <code>formik</code> library.</p>
  
  <p>I have tried to changing from </p>
  
  <pre><code>&lt;input
    type="checkbox"
    name="flag"
    checked={values.flag}
    onChange={handleChange}
    onBlur={handleBlur}
  /&gt;
  </code></pre>
  
  <p>to</p>
  
  <pre><code>&lt;input
    type="checkbox"
    name="flag"
    value={values.flag}
    onChange={handleChange}
    onBlur={handleBlur}
  /&gt;
  </code></pre>
  
  <p>but none is working.</p>
  
  <p>the component is as following</p>
  
  <pre><code>import { withFormik } from 'formik';
  ...
  
  const Form = props =&gt; (
    &lt;form&gt;
      &lt;input
        type="checkbox"
        name="flag"
        checked={props.values.flag}
        onChange={props.handleChange}
        onBlur={props.handleBlur}
      /&gt;
      &lt;input
        type="text"
        name="name"
        checked={props.values.name}
        onChange={props.handleChange}
        onBlur={props.handleBlur}
      /&gt;
    &lt;/form&gt;
  );
  
  const WrappedForm = withFormik({
    displayName: 'BasicForm',
  })(Form);
  
  export default WrappedForm;
  </code></pre>
  
  <p>It should change props.values when clicking checkbox.
  but it doesn't change props data at all.</p>
  
  <p>Btw, it changes props data when typing in text input box.
  This only happens with <code>checkbox</code>.</p>