Fix branding generation

mastodon.nix

@@ -3,17 +3,7 @@
 let
   secrets = import ./secrets.nix;
 
-  branding = ''
-    PATH=$PATH:${pkgs.librsvg}/bin:${pkgs.imagemagick}/bin \
-      RAILS_ENV=development rake branding:generate
-  '';
-
-  mastodon-lor-sh = (pkgs.mastodon.overrideAttrs(x: {
-    patchPhase = branding;
-    mastodon-modules = pkgs.mastodon.mastodon-modules.overrideAttrs(y: {
-      patchPhase = branding;
-    });
-  })).override {
+  mastodon-lor-sh = pkgs.mastodon.override {
     srcOverride = pkgs.applyPatches {
       src = pkgs.fetchgit {
         url = "https://github.com/mastodon/mastodon.git";
@@ -37,6 +27,7 @@ let
 
         ./patches/simple-form.patch
       ];
+      postPatch = (import ./branding.nix { pkgs = pkgs; }).branding;
     };
   };