switch pre_push to py3
switch pre_push to py3

Bug: chromium:1302992
Change-Id: I49c6fbe60fc58e9a150452322ebe9b81840579f7
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/3523881
Reviewed-by: John Chen <334fbfbb4df7c78f091ea1b77c69ca6ac731a3f3@chromium.org>
Commit-Queue: Egor Pasko <df62a37785f4466543d38b606e2821f2cbc99423@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult