Make Marcel whole again for git shortlog -sn

With this file you would get

    ❯ git shortlog -sn
      3802  Marcel Zwiers
       212  Rutger van Deelen
        23  Anthony Galassi
        22  Dominika Zemanovicova
         6  Stefano Moia
         ...

instead of current

    ❯ git shortlog -sn
      2907  MarsMellow
       495  Marcel Zwiers
       400  marcelzwiers
       212  Rutger van Deelen
        23  Anthony Galassi
        22  Dominika Zemanovicova
        ...

.mailmap

@@ -0,0 +1,3 @@
+Marcel Zwiers <mpzwiers@gmail.com>
+Marcel Zwiers <mpzwiers@gmail.com> <m.zwiers@donders.ru.nl>
+Marcel Zwiers <mpzwiers@gmail.com> <mpzwiers@gmail.com>