[Doxygen,Web] Replaced Mathjax script link.

https://www.mathjax.org/cdn-shutting-down/

Documentation/Doxyfile.in

@@ -1488,7 +1488,7 @@ MATHJAX_FORMAT         = HTML-CSS
 # The default value is: http://cdn.mathjax.org/mathjax/latest.
 # This tag requires that the tag USE_MATHJAX is set to YES.
 
-MATHJAX_RELPATH        = https://cdn.mathjax.org/mathjax/latest
+MATHJAX_RELPATH        = https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1
 
 # The MATHJAX_EXTENSIONS tag can be used to specify one or more MathJax
 # extension names that should be enabled during MathJax rendering. For example

web/layouts/partials/header.html

@@ -16,7 +16,7 @@
     });
   </script>
   <script type="text/javascript" async
-    src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-MML-AM_CHTML">
+    src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-MML-AM_CHTML">
   </script>
 
   <title>{{ .Title }}</title>