[fink-core] review fink#200 (allow zsh as SHELL in pathsetup script)

[Hanspeter N. <fi...@sn...>]

Can I please get a review for fink PR #200:
https://github.com/fink/fink/pull/200

This makes zsh a known shell inside the pathsetup script. 10.15 defaults 
to zsh, so we should make this work for new 10.15 users.

Hanspeter