MAINTAINERS: update email address

My personal email address has changed. Update it in the
MAINTAINERS file

Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 04e8d18..2bd095b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2111,7 +2111,7 @@
 BATMAN ADVANCED
 M:	Marek Lindner <mareklindner@neomailbox.ch>
 M:	Simon Wunderlich <sw@simonwunderlich.de>
-M:	Antonio Quartulli <antonio@meshcoding.com>
+M:	Antonio Quartulli <a@unstable.cc>
 L:	b.a.t.m.a.n@lists.open-mesh.org
 W:	http://www.open-mesh.org/
 S:	Maintained