security/zeek: Update to 4.0.0

This is the next Long-Term Support (LTS) major version:

https://github.com/zeek/zeek/releases/tag/v4.0.0
https://zeek.org/2020/12/15/zeek-4-0-release-candidate/

Support for the previous LTS (3.0.x) will end in about two months.

Reported by: Jon Siwek