[web] Updated MathJax.

web/layouts/partials/header.html

@@ -27,7 +27,7 @@
     });
   </script>
   <script async
-    src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-MML-AM_CHTML">
+    src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.7/MathJax.js?config=TeX-MML-AM_CHTML">
   </script>
 
 </head>