Updating MathJax CDN links

* doc/org.texi : Change reference to "cdn.mathjax.org" to "cdnjs.com",
  removing comment about no longer relevant terms of service.
* lisp/ox-html.el (org-html-mathjax-options) : Change link to
  appropriate cdnjs.com link to load MathJax.

Updating MathJax CDN links to reflect cdnjs.com as cdn.mathjax.org
will be disconitnued as of 30 April 2017.

TINYCHANGE

doc/org.texi

@@ -11660,10 +11660,8 @@ You could use @code{http} addresses just as well.
 @LaTeX{} math snippets (@pxref{@LaTeX{} fragments}) can be displayed in two
 different ways on HTML pages.  The default is to use
 @uref{http://www.mathjax.org, MathJax} which should work out of the box with
-Org@footnote{By default Org loads MathJax from
-@uref{http://docs.mathjax.org/en/latest/start.html#using-the-mathjax-content-delivery-network-cdn,
-MathJax.org}.  A link to the terms of service of the MathJax CDN can be found
-in the docstring of @code{org-html-mathjax-options}.}.  Some MathJax display
+Org@footnote{By default Org loads MathJax from @uref{https://cdnjs.com, cdnjs.com} as
+recommended by @uref{http://www.mathjax.org, MathJax}.}.  Some MathJax display
 options can be configured via @code{org-html-mathjax-options}, or in the
 buffer.  For example, with the following settings,
 @smallexample

lisp/ox-html.el

@@ -1153,7 +1153,7 @@ See `format-time-string' for more information on its components."
 ;;;; Template :: Mathjax
 
 (defcustom org-html-mathjax-options
-  '((path "http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS_HTML" )
+  '((path "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?config=TeX-AMS_HTML" )
     (scale "100")
     (align "center")
     (font "TeX")
@@ -1191,12 +1191,7 @@ You can also customize this for each buffer, using something like
 
 For further information about MathJax options, see the MathJax documentation:
 
-    http://docs.mathjax.org/
-
-Please note that by using the default CDN one must agree with
-MathJax CDN Terms of Service.
-
-    http://www.mathjax.org/mathjax-cdn-terms-of-service.html"
+  http://docs.mathjax.org/"
   :group 'org-export-html
   :package-version '(Org . "8.3")
   :type '(list :greedy t