Update AUTHORS and DONORS list

Thanks to all contributors and donors for making Godot possible!

Author: akien-mga

.mailmap

@@ -72,6 +72,7 @@ Liz Haas <27thLiz@gmail.com> <hinsbart@gmail.com>
 Liz Haas <27thLiz@gmail.com> <hinsbart@users.noreply.github.com>
 Liz Haas <27thLiz@gmail.com> <entenflugstuhl@gmail.com>
 Manuel Strey <manuel.strey@gmx.de>
+Marcel Admiraal <madmiraal@users.noreply.github.com>
 Marcelo Fernandez <marcelofg55@gmail.com>
 Marcin Zawiejski <dragmz@gmail.com>
 Marcus Elg <marcusaccounts@yahoo.se>