FIX: letter avatars to live in uploads directory, add last modified

app/controllers/user_avatars_controller.rb

@@ -29,6 +29,7 @@ class UserAvatarsController < ApplicationController
     end
 
     image = LetterAvatar.generate(params[:username].to_s, params[:size].to_i)
+    response.headers["Last-Modified"] = File.ctime(image).httpdate
     expires_in 1.year, public: true
     send_file image, disposition: nil
   end

lib/letter_avatar.rb

@@ -25,7 +25,7 @@ class LetterAvatar
 
 
     def cache_path
-      "tmp/letter_avatars/#{VERSION}"
+      "public/uploads/letter_avatars/#{VERSION}"
     end
 
     def generate(username, size, opts = nil)