Arxiv Iterator untars at the same path as download_dir which might fail due to lack of permissions

[praateekmahajan]

Curator/nemo_curator/stages/text/download/arxiv/iterator.py

Line 127 in bf694c9

with tempfile.TemporaryDirectory(dir=download_dir) as tmpdir, tarfile.open(file_path) as tf:

This cause failure inside benchmarks on the eos cluster where we don't have permissions

[nightcityblade]

Hi, I'd like to work on this. I'll submit a PR shortly.