use links friendly to China Mainland

README.md

@@ -34,12 +34,12 @@ var result = md.render('# Math Rulez! \n  $\\sqrt{3x-1}+(1+x)^2$');
 
 Include the KaTeX stylesheet in your html:
 ```html
-<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.10.0/katex.min.css">
+<link rel="stylesheet" href="https://cdn.bootcss.com/KaTeX/0.10.2/katex.min.css">
 ```
 
 If you're using the default markdown-it parser, I also recommend the [github stylesheet](https://github.com/sindresorhus/github-markdown-css):
 ```html
-<link rel="stylesheet" href="https://cdn.jsdelivr.net/github-markdown-css/2.2.1/github-markdown.css"/>
+<link rel="stylesheet" href="https://cdn.bootcss.com/github-markdown-css/3.0.1/github-markdown.min.css"/>
 ```
 
 `KaTeX` options can be supplied with the second argument to use.