maintainers: update my email address

lib/maintainers.nix

···
   meisternu = "Matt Miemiec <[e-mail]>";
   metabar = "Celine Mercier <[e-mail]>";
   mguentner = "Maximilian Güntner <[e-mail]>";
-  mic92 = "Jörg Thalheim <[e-mail]>";
+  mic92 = "Jörg Thalheim <[e-mail]>";
   michaelpj = "Michael Peyton Jones <[e-mail]>";
   michalrus = "Michal Rus <[e-mail]>";
   michelk = "Michel Kuhlmann <[e-mail]>";