git-absorb: add tomfitzhenry as maintainer

pkgs/applications/version-management/git-absorb/default.nix

···
     homepage = "https://github.com/tummychow/git-absorb";
     description = "git commit --fixup, but automatic";
     license = [ licenses.bsd3 ];
-    maintainers = [ ];
+    maintainers = with maintainers; [ tomfitzhenry ];
     mainProgram = "git-absorb";
   };
 }