Add ability to change offset for ready days

Now a client is able to change the offset for days and retry the request. This
is very useful in case of 1003 errors ('Pick-up service is not provided on
this day') caused by holidays.

An example code for client:

```ruby loop do
 response = request.post

  if response.error? && response.errors.map(&:code).any? { |code| code ==
'1003' }
   request.offset_days += 1
   next
 end

  return response.total_amount end
```