add ustc js cdn

layout/_partial/cdn_after_footer.ejs

@@ -1,5 +1,7 @@
 <% if (theme.cdn == "useso"){ %>
  <script src="//ajax.useso.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
+<% } else if (theme.cdn == "ustc") { %>
+ <script src="//ajax.lug.ustc.edu.cn/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
 <% } else { %>
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
 <% } %>