title: initialize a radio button in redux-form 6.8.0
body: <p>poor english
  i wanna make option A initial selection;</p>
  
  <p>i try this</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>const child = (props) =&gt; {
    return (
      &lt;div&gt;
        A:&lt;input {...props.input} type="radio" value="A" /&gt;
        B:&lt;input {...props.input} type="radio" value="B" /&gt;
      &lt;/div&gt;)
  }
  
  let Index = () =&gt; (
    &lt;form&gt;
      &lt;Field name="aaa" component={child} /&gt;
    &lt;/form&gt;
  )
  
  Index = reduxForm({
    form: 'slb',
    initialValues: {
      aaa: 'A',
    }
  })(Index);</code></pre>
  </div>
  </div>
  </p>
  
  <p>but this does not work</p>
  
  <p>please help me   thank you!</p>