adjust formula presentation

zh/8.md

 <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=default"></script>
-<script type="text/x-mathjax-config">
-    MathJax.Hub.Config({
-        tex2jax: {
-        inlineMath: [ ['$','$'], ["\\(","\\)"] ],
-        processEscapes: true
-        }
-    });
-</script>
+
 
 # 第八章 排序和选择