[DEV-8571] Update the MathJax CDN

The MathJax CDN stopped working in April 2017. I updated it to the
recommended CDN with the last version from April 2017 to ensure it works
like it used to work before the CDN stopped.

I added the checksum to ensure the content of the script.

RELEASES.md

@@ -13,6 +13,10 @@ TAME developers: Add new changes under a "NEXT" heading as part of the
 commits that introduce the changes.  To make a new release, run
 `tools/mkrelease`, which will handle updating the heading for you.
 
+NEXT
+====================
+- Update the CDN used to get MathJax.
+
 v17.6.2 (2020-10-01)
 ====================
 - Optionally include a "program.mk" file if it is present in the project's root

doc/Makefile.am

@@ -45,7 +45,7 @@ xsltexis: $(stexi)
 html-local:
 	find tame.html/ -name '*.html' -type f \
 		| xargs sed -i \
-		's#\(<script.*\)\?</body>#<script src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script></body>#'
+		's#\(<script.*\)\?</body>#<script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS-MML_HTMLorMML" integrity="sha512-tOav5w1OjvsSJzePRtt2uQPFwBoHt1VZcUq8l8nm5284LEKE9FSJBQryzMBzHxY5P0zRdNqEcpLIRVYFNgu1jw==" crossorigin="anonymous"></script></body>#'
 
 clean-local:
 	-rm -f $(stexi)

src/current/summary.xsl

@@ -214,8 +214,10 @@
           skipStartupTypeset: true,
         });
       </script>
-      <script type="text/javascript"
-        src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML">
+      <script
+        src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS-MML_HTMLorMML"
+        integrity="sha512-tOav5w1OjvsSJzePRtt2uQPFwBoHt1VZcUq8l8nm5284LEKE9FSJBQryzMBzHxY5P0zRdNqEcpLIRVYFNgu1jw=="
+        crossorigin="anonymous">
       </script>
 
       <!-- global functions for developers -->