quick fix best in place issue where empty values are posted accidentally.

The `ActiveRecord::Base#update_attributes` method is patched in order
to ignore empty string values.

https://trello.com/c/K4Uyw5QN/702-best-in-place-204-no-content-mit-unico
rn
fixing specs after patching `update_attributes`.

trello:
https://trello.com/c/K4Uyw5QN/702-best-in-place-204-no-content-mit-unico
rn