json file attempting to be written to root dir instead of public://

We are hosting with Pantheon, who only allows writing files to the public:// or private:// filesystem, not to the rest of the site files. There are a number of other hosts that work like this also, so it's not specific just to Pantheon I don't think.

The module is setting the JSON destination path to $response['data']['info']['site_name'] . "." . "json", but file_unmanaged_save_data's documentation says "This must be a stream wrapper URI."

Would it be possible to prefix that filename with `public://` in the module to allow it to support environments that only allow writing to the files directory? I tested it locally and it works fine, I will submit a patch momentarily.