title: Can't use "startIcon" & "endIcon" from <Button/> API of Material-UI
body: <p>Here is my simple React code for a single component but it keep throwing the same warning every-time I checked. Even when copy and past the example still same warning and the icon is nowhere to be seen. Please help!</p>
  
  <p><a href="https://i.stack.imgur.com/DsBta.png" rel="noreferrer">Link</a></p>
  
  <pre><code>import React, { Component } from 'react';
  import { Button } from '@material-ui/core';
  import AddIcon from '@material-ui/icons/Add';
  
  
  class AddWorkButton extends Component {
      constructor(props) {
          super(props);
          this.state = {  }
      }
      render() { 
          return (  
              &lt;React.Fragment&gt;
                  &lt;Button
                          variant="contained"
                          color="secondary"
                          startIcon={&lt;AddIcon/&gt;}
                  &gt;
                      TEST
                  &lt;/Button&gt;
              &lt;/React.Fragment&gt;
          );
      }
  }
  
  export default AddWorkButton;
  </code></pre>