use sentence case

tbrowder · web-flow · commit c853b2b5cca8 · 2018-07-07T19:42:04.000-05:00
diff --git a/doc/Language/concurrency.pod6 b/doc/Language/concurrency.pod6
@@ -2,7 +2,7 @@
 
 =TITLE Concurrency
 
-=SUBTITLE Concurrency and Asynchronous Programming
+=SUBTITLE Concurrency and asynchronous Programming
 
 In common with most modern programming languages, Perl 6 is designed to
 support parallelism, asynchronicity and L<concurrency|https://en.wikipedia.org/wiki/Concurrent_computing>.  Parallelism is about doing multiple things at once. I<Asynchronous programming>, which is sometimes called event driven or reactive
