fix: use zsh idioms and quote variables in shell config

- Use [[ ]] instead of [ ] for conditionals (zsh idiom)
- Quote variable expansions in ZINIT_HOME checks and dirname call
- Quote dollar-1 in mkcd function
- Remove extra blank line in .vimrc

Nightshift-Task: lint-fix
Nightshift-Ref: https://github.com/marcus/nightshift

.zshrc

@@ -36,8 +36,8 @@ zmodload zsh/stat
 
 # plugin manager
 ZINIT_HOME="${XDG_DATA_HOME:-${HOME}}/.zinit.git"
-[ ! -d "$ZINIT_HOME" ] && mkdir -p "$(dirname $ZINIT_HOME)"
-[ ! -d "$ZINIT_HOME/.git" ] && git clone https://github.com/zdharma-continuum/zinit.git "$ZINIT_HOME"
+[[ ! -d "$ZINIT_HOME" ]] && mkdir -p "$(dirname "$ZINIT_HOME")"
+[[ ! -d "$ZINIT_HOME/.git" ]] && git clone https://github.com/zdharma-continuum/zinit.git "$ZINIT_HOME"
 source "${ZINIT_HOME}/zinit.zsh"
 
 zinit light zsh-users/zsh-autosuggestions