notable: update license to unfree

Notable used to be released under AGPL-v3 until v1.5.x but is is now
nonfree.

See https://github.com/notable/notable/blob/master/SOURCE_CODE.md

pkgs/applications/misc/notable/default.nix

@@ -23,7 +23,7 @@ appimageTools.wrapType2 rec {
   meta = with lib; {
     description = "The markdown-based note-taking app that doesn't suck";
     homepage = "https://github.com/notable/notable";
-    license = licenses.agpl3;
+    license = licenses.unfree;
     platforms = [ "x86_64-linux" ];
     maintainers = with maintainers; [ dtzWill ];
   };