install: also configure ~/.zshenv
install: also configure ~/.zshenv

The default login shell for users on macOS 10.15 changed from bash to
zsh.  So while generally nonstandard we need to configure it to make nix
function out of the box on macOS.

rycee/nix,rycee/nix,NixOS/nix,rycee/nix,NixOS/nix,NixOS/nix,NixOS/nix,NixOS/nix,rycee/nix,rycee/nix