Updating an image end up deleting it

Hi,

I'm using ActiveAdmin, with CarrierWave (1.3.1) and Cloudinary (1.11.1) with Ruby 2.4.4 (same issue with ruby 2.5.3) and rails 4.2.1.

My issue is the following one:
If I create a new record with an image, it works fine and I can see this image on my Cloudinary dashboard. However, when I try to update my record for a new image, none of the two images are on my dashboard anymore, and the URL stored in my record's attribute leads to a `404`. However, the old version of the image is still available using the previous record's attribute's URL.

My guess is that there is either an issue with the cache like spotted in the issue #314, or an issue with carrierwave handling of cloudinary versions. However, the weirdest part is this deletion, and the fact that there is no trace of any image in my dashboard after update.

For more information, here are examples of my uploaders (feel free to ask for more information):

```ruby
class BaseUploader < CarrierWave::Uploader::Base
include Cloudinary::CarrierWave

cloudinary_transformation backup: Rails.env.production?

def public_id
"#{store_dir}/#{model.id}"
end

def extension_white_list
%w(jpg jpeg gif png)
end

def cache_dir
"#{Rails.root}/tmp/uploads"
end

def filename
"#{public_id}.#{file.extension}" if original_filename.present?
end

protected

def store_dir
"#{Rails.env}/#{model.class.to_s.underscore}/#{mounted_as}"
end
end

class TeamMemberPictureUploader < BaseUploader
version :thumb do
process resize_to_fill: [300, 300]
end
end

class TeamMember < ActiveRecord::Base
mount_uploader :picture, TeamMemberPictureUploader
end
```

---

While looking for similar issues, I came across #267. Maybe my issue is quite similar. But I don't get your answer:
> If you need your app to have both old and new images, then you'll need your app to be able to add more images rather than having a single updated one, and also make sure every new upload will assign a unique public ID to every upload.
> On the other hand, if you're ok with your app having only a single (latest) version of the image, but still want to not delete the old versions on your Cloudinary account, then you'll need to also make sure the public IDs are unique for each new upload.

What I want is to have one id associated to my record / environment / attribute. But I don't want it to change. The expected behavior is that the new picture will replace the old one.