title: Redux-form custom select not using first value
body: <p>I'm using react-redux and redux-form for my new project. When I create a custom select Field, it never passes the first option value (that is already "selected") to the handleSubmit function. Only when I manually select avalue, it passes the option value correctly. </p>
  
  <p>Custom select:</p>
  
  <pre><code>const Select = ({ input, options, disabled }) =&gt; (
    &lt;div&gt;
      &lt;select {...input} disabled={disabled}&gt;
        { options.map(option =&gt;
          &lt;option key={option.value} value={option.value}&gt;
            {option.label}
          &lt;/option&gt;
        )}
      &lt;/select&gt;
    &lt;/div&gt;
  );
  </code></pre>
  
  <p>Form Component:</p>
  
  <pre><code>function RegisterForm({ handleSubmit, titles }) {
    return (
      &lt;form onSubmit={handleSubmit}&gt;
        &lt;label htmlFor="title"&gt;Title&lt;/label&gt;
        &lt;Field name="title" options={titles} component={Select} /&gt;
  
        &lt;button type="submit"&gt;Submit&lt;/button&gt;
      &lt;/form&gt;
    );
  }
  
  RegisterForm.propTypes = {
    handleSubmit: PropTypes.func.isRequired,
    titles: PropTypes.array.isRequired,
  };
  
  export default reduxForm({
    form: 'register'
  })(RegisterForm);
  </code></pre>
  
  <p>Do I have to initialize the select from the redux state? Or is there another way to force the first value to be the initial value?</p>
  
  <p>Thanks in advance!</p>