title: prop-types doesn't work in React Native App
body: <p>PropTypes doesn't work for me in React Native. I think the code is fine but this way RN doesn't warn me about Prop-types violations and defaults props doesn't even works, I don't know why. </p>
  
  <p>My npm packages: 
      "prop-types": "^15.7.2",
      "react": "16.8.6",
      "react-native": "0.60.4"</p>
  
  <pre><code>import React from "react";
  import { Text } from "react-native";
  import PropTypes from "prop-types";
  
  import { Modal } from "@ant-design/react-native";
  
  import config from "./config";
  import styles from "./styles";
  
  const ModalAlert = ({
    title,
    content,
    okeyCallback,
    cancelCallBack
  }) =&gt; {
    const renderTitle = title =&gt; &lt;Text style={styles.title}&gt;{title}&lt;/Text&gt;;
  
    const renderContent = content =&gt; (
      &lt;Text style={styles.content}&gt;{content}&lt;/Text&gt;
    );
  
    const renderBtn = text =&gt; &lt;Text style={styles.btn}&gt;{text}&lt;/Text&gt;;
  
    cancelCallBack
      ? Modal.alert(renderTitle(title), renderContent(content), [
          {
            text: renderBtn(config.texts.confirmText),
            onPress: () =&gt;
              okeyCallback === null ? console.log("Ok pressed") : okeyCallback()
          },
          {
            text: renderBtn(config.texts.cancelText),
            onPress: () =&gt;
              cancelCallBack === null
                ? console.log("Cancel pressed")
                : cancelCallBack()
          }
        ])
      : Modal.alert(renderTitle(title), renderContent(content), [
          {
            text: renderBtn(config.texts.confirmText),
  
            onPress: () =&gt;
              okeyCallback === null ? console.log("Ok pressed") : okeyCallback()
          }
        ]);
  };
  
  ModalAlert.PropTypes = {
    title: PropTypes.string.isRequired,
    content: PropTypes.string.isRequired,
    okeyCallback: PropTypes.func,
    cancelCallBack: PropTypes.func
  };
  
  ModalAlert.defaultProps = {
    title: "deafult"
  };
  
  export { ModalAlert };
  </code></pre>