Add back current_files.push (fix s3_uploads_complete callback)

For some reason `current_files.push data` was removed in this
[commit](https://github.com/waynehoover/s3_direct_upload/commit/c0e96b80f29f4525767d68aca5ef1a9b133c57b3)
which breaks s3_uploads_complete (it gets called on first file 
completion instead of last).