update font spec doc

site/static/style.css

@@ -543,7 +543,7 @@ footer ul li > a {
 
 .markdown h1 { font-size: 28px; }
 .markdown h2 { font-size: 24px; }
-.markdown h3 { font-size: 20px; }
+.markdown h3 { font-size: 18px; }
 .markdown h4 { font-size: 16px; }
 .markdown h5 { font-size: 14px; }
 .markdown h6 { font-size: 12px; }

spec/font.md

@@ -11,7 +11,7 @@
 
 - 中文字体族：
 
-   <img src="https://t.alipayobjects.com/images/T1NrdhXghnXXXXXXXX.png" width="100%">
+   <img src="https://os.alipayobjects.com/rmsportal/OKbesWXtRMCNGmO.png" width="100%">
 
 - 英文文字体族：
 
@@ -20,7 +20,7 @@
 字体家族 css 代码如下：
 
 ```css
-font-family: "Helvetica Neue",Helvetica,"Hiragino Sans GB","STHeitiSC-Light","Microsoft YaHei","微软雅黑",Arial,sans-serif;
+font-family: "Helvetica Neue",Helvetica,"PingFang SC","Hiragino Sans GB","Microsoft YaHei","微软雅黑",Arial,sans-serif;
 ```
 
 ## 字体使用规范