Fix mathjax not able to render issue

public/js/extra.js

@@ -904,7 +904,14 @@ md.use(require('markdown-it-mark'));
 md.use(require('markdown-it-ins'));
 md.use(require('markdown-it-sub'));
 md.use(require('markdown-it-sup'));
-md.use(require('markdown-it-mathjax'));
+md.use(require('markdown-it-mathjax')({
+    beforeMath: '<span class="mathjax raw">',
+    afterMath: '</span>',
+    beforeInlineMath: '<span class="mathjax raw">\\(',
+    afterInlineMath: '\\)</span>',
+    beforeDisplayMath: '<span class="mathjax raw">\\[',
+    afterDisplayMath: '\\]</span>'
+}));
 md.use(require('markdown-it-imsize'));
 
 md.use(require('markdown-it-emoji'), {