fsmonitor: migrate Python ABCs from collections to collections.abc
The Collections Abstract Base Classes in the collections module are
deprecated since Python 3.3 in favor of collections.abc, and removed
in Python 3.10.
import hashlib
try:
from ..thirdparty import sha1dc # pytype: disable=import-error
sha1 = sha1dc.sha1
except (ImportError, AttributeError):
sha1 = hashlib.sha1