Fix missing responseText when json is returned

I found this problem in the remember library. It may be because I'm using JSONP or maybe just my version of jQuery, but `jqxhr.responseText` is not being set. This means when you try to parse it later on to get the remember token, an exception is thrown.

Rather than parsing it, I've stored the json that's returned from the AJAX and used that directly, which stops an extra parse and works for me.

I've not included a .min.js because I figure you probably have a process that you like for that, but let me know if you want me to.

Thanks again for a great library!