Revert "Remove maintainership"

I'm baaaaack!

This patch reverts my patch where I removed myself as maintainer because
of my traveling. I'm back now and I want to maintain these packages
again.

This reverts commit ce1c1e3093.

pkgs/development/python-modules/pygraphviz/default.nix

@@ -32,6 +32,6 @@ buildPythonPackage rec {
     description = "Python interface to Graphviz graph drawing package";
     homepage = https://github.com/pygraphviz/pygraphviz;
     license = licenses.bsd3;
-    maintainers = with maintainers; [ ];
+    maintainers = with maintainers; [ matthiasbeyer ];
   };
 }