Stop using UrlVariables since it is un-ordered.

I have a real-world use case for this. I am creating a file on S3 but my data is plain text generated by JavaScript (i.e. not a blob). S3 REQUIRES the file to come last. But even if I set it last it is still coming much earlier causing a bad request. By keeping the params sorted I have control over what param is encoded where if it matters to me.