Update maintainer list

[skip ci]

libs/maintainers.txt

@@ -85,7 +85,7 @@ lambda2               Peter Dimov <pdimov -at- gmail.com>
 leaf                  Emil Dotchevski
 lexical_cast          Antony Polukhin <antoshkka -at- gmail.com>
 local_function        Lorenzo Caminiti <lorcaminiti -at- gmail.com>
-locale                Artyom Beilis <artyomtnk -at- yahoo.com>
+locale                Artyom Beilis <artyomtnk -at- yahoo.com>, Alexander Grund <alex -at- grundis.de>
 lockfree              Tim Blechmann <tim -at- klingt.org>
 log                   Andrey Semashev <andrey.semashev -at- gmail.com>
 logic                 Douglas Gregor <dgregor -at- cs.indiana.edu>