xresources: use profileExtra instead of initExtra

The initExtra code is executed after systemd graphical-session.target
starts, which means graphical applications started by
graphical-session.target cannot get these X settings.

modules/xresources.nix

@@ -99,6 +99,6 @@ in {
         '';
       };
 
-      xsession.initExtra = xrdbMerge;
+      xsession.profileExtra = xrdbMerge;
     };
 }