Standardize strip with resy of application. Without to_s, causes erro…

…rs like "undefined method `strip' for image/bmp:MIME::Type".

lib/tasks/paperclip.rake

@@ -47,7 +47,7 @@ namespace :paperclip do
         Paperclip.each_instance_with_attachment(klass, name) do |instance|
           if file = instance.send(name).to_file(:original)
             instance.send("#{name}_file_name=", instance.send("#{name}_file_name").strip)
-            instance.send("#{name}_content_type=", file.content_type.strip)
+            instance.send("#{name}_content_type=", file.content_type.to_s.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)