correct gzip files if they exist as well

lib/tasks/assets.rake

@@ -3,8 +3,27 @@ namespace :assets do
   task :precompile do
     css_files = Dir['public/assets/*.css']
     css_files.each do | file |
+      # replace url(/assets/*) with url(./*)
       puts "Fixing #{file}"
       system "sed", "-i", "-e", 's/url(\([\"\']\?\)\/assets\//url(\1.\//g', file
+
+      # rewrite the corresponding gzip file (if it exists)
+      gzip = "#{file}.gz"
+      if File.exist?(gzip)
+        puts "Fixing #{gzip}"
+
+        FileUtils.rm(gzip)
+        mtime = File.stat(file).mtime
+
+        File.open(gzip, 'wb+') do |f|
+          gz = Zlib::GzipWriter.new(f, Zlib::BEST_COMPRESSION)
+          gz.mtime = mtime
+          gz.write IO.binread(file)
+          gz.close
+
+          File.utime(mtime, mtime, f.path)
+        end
+      end
     end
   end
 end