title: Warning: Failed propType: Calling PropTypes validators directly is not supported
body: <p>I've been trying to add grid to my react project but when I load the page it gives me an error:</p>
  
  <p><code>Warning: Failed propType: Calling PropTypes validators directly is not supported by the `prop-types` package. Use `PropTypes.checkPropTypes()` to call them. Read more at https://github.com/facebook/prop-types/blob/master/README.md#difference-from-reactproptypes-dont-call-validator-functions Check the render method of `GridTest`.</code></p>
  
  <p>Tried using <code>antd</code> and <code>react-flexbox-grid</code>, but both libraries produce the same error.</p>
  
  <p>Code:</p>
  
  <pre><code>    import React, { Component } from 'react';
      import {Grid, Row, Col} from 'react-flexbox-grid';
  
      export default class GridTest extends Component {
          render() {
            return (
              &lt;Grid&gt;
                &lt;Row&gt;
                  &lt;Col xs={6} md={3}&gt;Hello, world!&lt;/Col&gt;
                &lt;/Row&gt;
              &lt;/Grid&gt;
            );
          }
      }
  </code></pre>
  
  <p>Any suggestions on how to fix this? I think problem might be caused by external lib not bundling <code>prop-types</code> or something?..</p>