change case of HTML for consistency on the page

Author: tbrowder

doc/Language/about.pod6

@@ -18,7 +18,7 @@ GitHub|https://github.com/perl6/doc>.
 The information in this particular document is a quick overview of the process
 described in more detail in L<CONTRIBUTING on GitHub|https://github.com/perl6/doc/CONTRIBUTING.md>.
 This document also provides a short introduction to writing the Perl 6
-POD files which produce the rendered pages in html or other formats.
+POD files which produce the rendered pages in HTML or other formats.
 
 =head1 Structure