title: agGroupCellRenderer not found
body: <p>I upgraded the ag-grid &amp; ag-grid-react to 14.2.0, but I still get this warning:</p>
  
  <blockquote>
    <p>ag-grid: Looking for component [agGroupCellRenderer] but it wasn't found.</p>
  </blockquote>
  
  <p>My column definitions:</p>
  
  <pre><code>let columnDefs = [
      {headerName: 'Name', field: 'userName', width:163, cellRenderer:'agGroupCellRenderer'},
      {headerName: 'Job Title', field: 'jobTitle', width:143},
  ]
  </code></pre>
  
  <p>What am I missing here? </p>