Correctly add packaging as a dependency

[skasai5296]

This is a follow-up for facebookresearch/faiss#3191.

Issue

Importing faiss fails at runtime;

>>> import faiss
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../site-packages/faiss/__init__.py", line 16, in <module>
    from .loader import *
  File ".../site-packages/faiss/loader.py", line 6, in <module>
    from packaging.version import Version
ModuleNotFoundError: No module named 'packaging'

[kyamagu]

LGTM