title: Office UI Fabric ReactJS Dropdown Accessibility issue
body: <p>I am using Office UI Fabric Dropdown in React.js. I am testing the application for accessibility issues using Keros for Web. </p>
  
  <p>It is showing this issue for dropdowns:</p>
  
  <pre><code>aria-valid-attr-value: ARIA attributes must conform to valid values
  Fix the following: Invalid ARIA attribute value: aria-labelledby="usercountryRegion-label" 
  Snippet: &lt;div data-is-focusable="true" id="usercountryRegion" tabindex="0" aria-expanded="false" role="listbox" aria-labelledby="usercountryRegion-label" aria-describedby="usercountryRegion-option" aria-activedescendant="usercountryRegion-option" name="country" class="ms-Dropdown root_aecb6435"&gt;
  </code></pre>
  
  <p>I searched for some answer and all I got is "Ensure the value inside each attribute is spelled correctly and corresponds to a valid value.", but I could not find a solution to this.</p>