users-guide: Override mathjax_path

The Mathjax CDN no longer exists. Use CDNJS instead.

See #15006.

Test Plan: Build HTML users guide, see whether math is rendered.

Reviewers: alpmestan

Reviewed By: alpmestan

Subscribers: thomie, carter

GHC Trac Issues: #15006

Differential Revision: https://phabricator.haskell.org/D4603

(cherry picked from commit 803178a5)

docs/users_guide/conf.py

@@ -57,6 +57,9 @@ html_use_smartypants = True
 html_use_opensearch = 'https://downloads.haskell.org/~ghc/master/users-guide'
 html_show_copyright = True
 
+# See GHC #15006
+mathjax_path = 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js'
+
 # If true, an OpenSearch description file will be output, and all pages will
 # contain a <link> tag referring to it.  The value of this option must be the
 # base URL from which the finished HTML is served.