Use local source tree for zkg in shiv command

[ckreibich]

In my local Zeek tree I swapped the auxil/package-manager submodule out for some of our current branch work, and after installing I noticed that the zkg version kept reporting

$ zkg --version
zkg 3.1.0

That is, the local version of zkg made no difference to the install. I think that's because simply passing zkg to shiv causes it to just pass that on to pip install, which then pulls it down from PyPI, where 3.1.0 is the latest.

The first thing I noticed was that I kept getting

Using cached zkg-3.1.0-py2.py3-none-any.whl (72 kB)

in the build, which I eventually tracked down to the contents of ~/.cache/pip — not obvious. After blowing that away, I noticed it still did

Downloading zkg-3.1.0-py2.py3-none-any.whl (72 kB)

which eventually led me to this tweak after reading up on shiv. Seems to be working for me.

@bbannier fyi

[bbannier]

Dio mio, thanks!