title: Material UI tooltip doesn't display on custom component, despite spreading props to that component
body: <p>I am having difficulties making the Material UI tooltip actually appear when hovering over a component. As far as I can tell, I am doing about the simplest implementation of the tooltip component: I import it directly (no custom styles or anything else yet), and I wrap it around another component that spreads out its props at the top level. </p>
  
  <p>From reading the documentation it should be that simple, but it is not appearing on hover, and in the React DevTools I see that the anchorEl prop of  is undefined.</p>
  
  <pre><code>import Tooltip from '@material-ui/core/Tooltip';
  
  const containerComponent = () =&gt; (
      &lt;Tooltip text="Planner"&gt;&lt;PlannerIcon /&gt;&lt;/Tooltip&gt;
  )
  </code></pre>
  
  <p>PlannerIcon.js</p>
  
  <pre><code>const PlannerIcon = (props) =&gt; (
    &lt;Icon xmlns="http://www.w3.org/2000/svg" viewBox="0 0 18 18"
      {...props}
    &gt;
      &lt;path d="M14.71,3.11V14.88H2.94V3.11H14.71m1-1H1.94V15.88H15.71V2.11Z"/&gt;
      &lt;line x1="1.94" y1="9" x2="15.71" y2="9" strokeMiterlimit="10"/&gt;
      &lt;line x1="8.83" y1="2.12" x2="8.83" y2="15.77" strokeMiterlimit="10"/&gt;
    &lt;/Icon&gt;
    );
  </code></pre>