maintainers: update wiki url for the security subsystem

Update the wiki url for the security subsystem to:

http://kernsec.org/Signed-off-by: James Morris <james.l.morris@oracle.com>

MAINTAINERS

@@ -5956,7 +5956,7 @@ SECURITY SUBSYSTEM
 M:	James Morris <james.l.morris@oracle.com>
 L:	linux-security-module@vger.kernel.org (suggested Cc:)
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git
-W:	http://security.wiki.kernel.org/
+W:	http://kernsec.org/
 S:	Supported
 F:	security/