Fix MetadataError to_s formatting (#4394)

Author: philippthun

app/models/helpers/metadata_error.rb

@@ -9,7 +9,7 @@ def self.none
     end
 
     def to_s
-      "#<MetadataError is_valid:#{is_valid?} message:#{message}"
+      "#<MetadataError is_valid:#{is_valid?} message:#{message}>"
     end
   end
 end