Fixing PropTypes warning messages (#2670)

* Fixing PropTypes warning message

React recently started warning on the upcoming deprecation of
React.PropTypes, the new approach is to use the `prop-types`
npm package instead.

* Fixing the tests

superset/assets/javascripts/SqlLab/components/DataPreviewModal.jsx

@@ -1,4 +1,5 @@
 import React from 'react';
+import PropTypes from 'prop-types';
 import { bindActionCreators } from 'redux';
 import { connect } from 'react-redux';
 import { Modal } from 'react-bootstrap';
@@ -7,10 +8,10 @@ import * as Actions from '../actions';
 import ResultSet from './ResultSet';
 
 const propTypes = {
-  queries: React.PropTypes.object,
-  actions: React.PropTypes.object,
-  showDataPreviewModal: React.PropTypes.bool,
-  dataPreviewQueryId: React.PropTypes.string,
+  queries: PropTypes.object,
+  actions: PropTypes.object,
+  showDataPreviewModal: PropTypes.bool,
+  dataPreviewQueryId: PropTypes.string,
 };
 
 class DataPreviewModal extends React.PureComponent {