Update maintainer list

[skip ci]

libs/maintainers.txt

@@ -26,6 +26,7 @@ bind                  Peter Dimov <pdimov -at- gmail.com>
 callable_traits       Barrett Adair <barrettellisadair -at- gmail.com>
 charconv              Matt Borland <matt -at- mattborland.com>
 chrono                Vicente J. Botet Escriba <vicente.botet -at- wanadoo.fr>
+chrono/stopwatch      Vicente J. Botet Escriba <vicente.botet -at- wanadoo.fr>
 circular_buffer       Jan Gaspar <jano_gaspar -at- yahoo.com>
 cobalt                Klemens Morgenstern <klemens -dot- d -dot- morgenstern -at- gmail.com>
 compat                Peter Dimov <pdimov -at- gmail.com>