treewide: fix shellcheck issues

I used 'bash' for zsh files, since that's the closest and `shell=zsh` is
not supported [1].

[1]: https://github.com/koalaman/shellcheck/issues/809

bootstrap.sh

@@ -1,5 +1,6 @@
 #!/usr/bin/env nix-shell
 #! nix-shell -i bash -p bitwarden-cli git gnupg jq nix
+# shellcheck shell=bash
 
 # Command failure is script failure
 set -e
@@ -10,7 +11,6 @@ BOLD_GREEN="\e[0;1;32m"
 
 RESET="\e[0m"
 
-DEST="$HOME/.config/nixpkgs"
 BW_SESSION=""
 
 warn() {

home/zsh/completion-styles.zsh

@@ -1,4 +1,7 @@
+# shellcheck shell=bash
+
 # Style the completion a bit
+# shellcheck disable=2086,2296
 zstyle ':completion:*' list-colors ${(s.:.)LS_COLORS}
 # Show a prompt on selection
 zstyle ':completion:*' select-prompt '%SScrolling active: current selection at %p%s'
@@ -21,6 +24,7 @@ zstyle ':completion:*:*:(^rm):*:*files' ignored-patterns '*?.o' '*?.c~' '*?.old'
 
 # command for process lists, the local web server details and host completion
 # on processes completion complete all user processes
+# shellcheck disable=2016
 zstyle ':completion:*:processes' command 'ps -au$USER'
 
 # Completion formatting and messages

home/zsh/extra-mappings.zsh

@@ -1,4 +1,4 @@
-# shellcheck disable=2154
+# shellcheck shell=bash
 
 # Fix Ctrl+u killing from the cursor instead of the whole line
 bindkey '^u' backward-kill-line

home/zsh/options.zsh

@@ -1,3 +1,5 @@
+# shellcheck shell=bash
+
 # Show an error when a globbing expansion doesn't find any match
 setopt nomatch
 # List on ambiguous completion and Insert first match immediately

hosts/nixos/porthos/install.sh

@@ -30,6 +30,7 @@ swapon /dev/sda2
 
 apt install sudo
 useradd -m -G sudo setupuser
+# shellcheck disable=2117
 su setupuser
 
 cat << EOF
@@ -37,7 +38,7 @@ cat << EOF
 curl -L https://nixos.org/nix/install | sh
 . $HOME/.nix-profile/etc/profile.d/nix.sh
 nix-channel --add https://nixos.org/channels/nixos-20.09 nixpkgs
-sudo `which nixos-generate-config` --root /mnt
+sudo "$(which nixos-generate-config)" --root /mnt
 
 # Change uuids to labels
 vim /mnt/etc/nixos/hardware-configuration.nix