Update maintainer list.

libs/maintainers.txt

@@ -43,6 +43,7 @@ dll                   Antony Polukhin <antoshkka -at- gmail.com>
 dynamic_bitset        Jeremy Siek <jeremy.siek -at- gmail.com>
 endian                Beman Dawes <bdawes -at- acm.org>
 exception             Emil Dotchevski <emil -at- revergestudios.com>
+fiber                 Oliver Kowalke <oliver.kowalke -at- gmail.com>
 filesystem            Beman Dawes <bdawes -at- acm.org>
 flyweight             Joaquin M Lopez Munoz <joaquin.lopezmunoz -at- gmail.com>
 foreach               Eric Niebler <eric -at- boostpro.com>