The `#store` return value is always true, not sure why.

As the only documentation was the code, I copied the behavior of https://github.com/carrierwaveuploader/carrierwave/blob/master/lib/carrierwave/storage/fog.rb#L324 and https://github.com/carrierwaveuploader/carrierwave/blob/master/lib/carrierwave/storage/fog.rb#L415 that seems to be good enough.