doc(Modal): 重构模态框组件文档

Author: nullptr-z

packages/core/src/Modal/README.md

@@ -8,7 +8,6 @@ Modal 模态框
 
 ### 基础示例
 
-
 ```jsx  mdx:preview
 import React, { useState, Fragment } from 'react';
 import { View, Text, SafeAreaView } from 'react-native';