Make expiring_url return a string instead of a url object.

This is more consistent to the normal url method.

Author: Sven Felix Oberquelle

lib/paperclip/storage/azure.rb

@@ -92,7 +92,7 @@ def expiring_url(time = 3600, style_name = default_style)
                                            permissions:  'r',
                                            start:        (Time.now - (5 * 60)).utc.iso8601,
                                            expiry:       (Time.now + time).utc.iso8601
-          azure_interface.generate_uri uri.path, CGI::parse(uri.query || "")
+          azure_interface.generate_uri(uri.path, CGI::parse(uri.query || "")).to_s
         else
           url(style_name)
         end