fix invalid HTML in 2020/ferguson2/README.md

Ran `bin/readme2index.sh -v 1 2020/ferguson2` to perform the above.

2020/ferguson2/README.md

@@ -714,7 +714,7 @@ greatly.
 
 
 <div id="portability">
-### <a  href="#toc">Portability
+### <a  href="#toc">Portability</a>
 </div>
 
 I have tested it under macOS, Fedora and CentOS Linux and all seems okay under

2020/ferguson2/index.html

@@ -905,7 +905,7 @@ be found in the source code verbatim and you could confirm it by looking them
 up; however much more would have to be done in order to get them to work, than
 to just put the strings in. Again the way I set things up complicates this
 greatly.</p>
-<h3 id="portability"><a  href="#toc">Portability</h3>
+<h3 id="portability"><a  href="#toc">Portability</a></h3>
 <p>I have tested it under macOS, Fedora and CentOS Linux and all seems okay under
 these platforms. When I was in the final stages of obfuscation I made an error
 somehow (or else maybe the vim formatting caused a problem - I have seen this