title: Material Ui - Add required attribute to a TextField in "select" mode
body: <p>I am trying to make "required" a TextField in select mode.
  I tried to add <code>required</code> prop like in this snippet, but this does not block the submit event if I haven't select anything. Although it adds the '*' to the label.</p>
  
  <p>Please check this <a href="https://codesandbox.io/s/6jxvvq9463" rel="noreferrer">sandbox</a></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>&lt;TextField
    id="select-currency"
    select
    label="Select"
    value={this.state.currency}
    onChange={this.handleChange("currency")}
    required
  &gt;
    {currencies.map(option =&gt; (
      &lt;MenuItem key={option.value} value={option.value}&gt;
        {option.label}
      &lt;/MenuItem&gt;
    ))}
  &lt;/TextField&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>UPDATE: (Clarification really)
  I am talking about html5 validation. In the sandbox example there are Select and Text fields, setting the text field as required will block the submit event and displays a native html5 error saying "this field is required", this is not the case if the field is "select".</p>