MAINTAINERS: Migrate oxnas list to groups.io

The linux-oxnas migrates from tuxfamily to groups.io for a simpler
administration and maintainance.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

MAINTAINERS

@@ -1743,7 +1743,7 @@ F:	arch/arm/mach-orion5x/ts78xx-*
 ARM/OXNAS platform support
 M:	Neil Armstrong <narmstrong@baylibre.com>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
-L:	linux-oxnas@lists.tuxfamily.org (moderated for non-subscribers)
+L:	linux-oxnas@groups.io (moderated for non-subscribers)
 S:	Maintained
 F:	arch/arm/mach-oxnas/
 F:	arch/arm/boot/dts/ox8*.dts*