Fix destructuring-style PropTypes references

Reviewed By: bvaughn

Differential Revision: D5600808

fbshipit-source-id: 8634d199b3480ea5c65ca095a51278efc3c44bcd

Libraries/Components/Navigation/NavigatorIOS.ios.js

@@ -141,7 +141,8 @@ type Event = Object;
  * navigates to. `initialRoute` represents the first route in your navigator.
  *
  * ```
- * import React, { Component, PropTypes } from 'react';
+ * import PropTypes from 'prop-types';
+ * import React, { Component } from 'react';
  * import { NavigatorIOS, Text } from 'react-native';
  *
  * export default class NavigatorIOSApp extends Component {