lib.maintainers: add Michiel Leenaars (close #13516)

As suggested in https://github.com/NixOS/nixpkgs/pull/13504 by @hrdinka.

leenaars 6c916515 c39cc6cd

Changed files
+1
lib
+1
lib/maintainers.nix
···
lassulus = "Lassulus <lassulus@gmail.com>";
layus = "Guillaume Maudoux <layus.on@gmail.com>";
lebastr = "Alexander Lebedev <lebastr@gmail.com>";
+
leenaars = "Michiel Leenaars <ml.software@leenaa.rs>";
leonardoce = "Leonardo Cecchi <leonardo.cecchi@gmail.com>";
lethalman = "Luca Bruno <lucabru@src.gnome.org>";
lewo = "Antoine Eiche <lewo@abesis.fr>";