Add support for uploading base64 images

[feliperenan]

Hi 👋🏻

I have this case in my current project so that I have to upload images that are stored as base64 in my DB to Cloudinary. I had to apply this fix in order to get it working.

Does that sounds good to you guys? If you say so, I'm happy to improve the code and add tests for it.

Thanks for the library 💪🏻