docs: update image demo (ant-design#53974)

Author: kiner-tang

components/image/__tests__/__snapshots__/demo-extend.test.ts.snap

@@ -376,7 +376,7 @@ exports[`renders components/image/demo/placeholder.tsx extend context correctly
     >
       <img
         class="ant-image-img"
-        src="https://zos.alipayobjects.com/rmsportal/jkjgkEfvpUPVyRjUImniVslZfWPnJuuZ.png?undefined"
+        src="https://zos.alipayobjects.com/rmsportal/jkjgkEfvpUPVyRjUImniVslZfWPnJuuZ.png?1479772800000"
         width="200"
       />
       <div

components/image/__tests__/__snapshots__/demo.test.ts.snap

@@ -365,7 +365,7 @@ exports[`renders components/image/demo/placeholder.tsx correctly 1`] = `
     >
       <img
         class="ant-image-img"
-        src="https://zos.alipayobjects.com/rmsportal/jkjgkEfvpUPVyRjUImniVslZfWPnJuuZ.png?undefined"
+        src="https://zos.alipayobjects.com/rmsportal/jkjgkEfvpUPVyRjUImniVslZfWPnJuuZ.png?1479772800000"
         width="200"
       />
       <div

components/image/demo/placeholder.tsx

@@ -2,7 +2,7 @@ import React, { useState } from 'react';
 import { Button, Image, Space } from 'antd';
 
 const App: React.FC = () => {
-  const [random, setRandom] = useState<number>();
+  const [random, setRandom] = useState<number>(Date.now());
 
   return (
     <Space size={12}>