Use `save(:validate => false)` since `save(false)` is deprecated in 3.x

Closes #481

lib/tasks/paperclip.rake

@@ -44,7 +44,11 @@ namespace :paperclip do
             instance.send("#{name}_file_name=", instance.send("#{name}_file_name").strip)
             instance.send("#{name}_content_type=", file.content_type.strip)
             instance.send("#{name}_file_size=", file.size) if instance.respond_to?("#{name}_file_size")
+            if Rails.version >= "3.0.0"
+              instance.save(:validate => false)
+            else
               instance.save(false)
+            end
           else
             true
           end