weechatScripts.wee-slack: replace myself as maintainer with willibutz

We just talked about this in private. I don't use this anymore for
various reasons, but willibutz is a wee-slack user and
definetely a well-qualified replacement here.

pkgs/applications/networking/irc/weechat/scripts/wee-slack/default.nix

@@ -31,7 +31,7 @@ stdenv.mkDerivation rec {
   meta = with stdenv.lib; {
     homepage = https://github.com/wee-slack/wee-slack;
     license = licenses.mit;
-    maintainers = with maintainers; [ ma27 ];
+    maintainers = with maintainers; [ willibutz ];
     description = ''
       A WeeChat plugin for Slack.com. Synchronizes read markers, provides typing notification, search, etc..
     '';