NewPane: and NewTab: don't use CWD.

[a-kenji]

Basic information
zellij --version: main - 0.20.0
uname -av or ver(Windows):
Linux 5.10.76 #1-NixOS SMP Wed Oct 27 07:56:57 UTC 2021 x86_64 GNU/Linux
alacritty --version: 0.9.0
fish: 3.3.1

Further information
Reproduction steps, noticeable behavior, related issues, etc

Steps:

• open zellij
• go to a directory
• open tab / pane

The pane or tab is now not opened in the current working directory.

I am not sure if this is because I am using fish, because it works in bash for me.
Or because I have fish specified in default_shell