Migrate nord.tmux file to ZSH shell

Author: moritzdietz

nord.tmux

@@ -1,5 +1,12 @@
-# Copyright (c) 2016-present Sven Greb <[email protected]>
-# This source code is licensed under the MIT license found in the license file.
+#!/usr/bin/env zsh
+# Copyright (C) 2017-present Arctic Ice Studio <[email protected]>
+# Copyright (C) 2017-present Sven Greb <[email protected]>
+
+# Project:    Nord tmux
+# Repository: https://github.com/arcticicestudio/nord-tmux
+# License:    MIT
+# References:
+#   https://tmux.github.io
 
 NORD_TMUX_COLOR_THEME_FILE=src/nord.conf
 NORD_TMUX_VERSION=0.3.0
@@ -8,7 +15,7 @@ NORD_TMUX_STATUS_CONTENT_NO_PATCHED_FONT_FILE="src/nord-status-content-no-patche
 NORD_TMUX_STATUS_CONTENT_OPTION="@nord_tmux_show_status_content"
 NORD_TMUX_STATUS_CONTENT_DATE_FORMAT="@nord_tmux_date_format"
 NORD_TMUX_NO_PATCHED_FONT_OPTION="@nord_tmux_no_patched_font"
-_current_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+_current_dir="${0:a:h}"
 
 __cleanup() {
   unset -v NORD_TMUX_COLOR_THEME_FILE NORD_TMUX_VERSION
@@ -28,7 +35,7 @@ __load() {
   local no_patched_font=$(tmux show-option -gqv "$NORD_TMUX_NO_PATCHED_FONT_OPTION")
   local date_format=$(tmux show-option -gqv "$NORD_TMUX_STATUS_CONTENT_DATE_FORMAT")
 
-  if [ "$(tmux show-option -gqv "clock-mode-style")" == '12' ]; then
+  if [[ "$(tmux show-option -gqv "clock-mode-style")" == '12' ]]; then
     tmux set-environment -g NORD_TMUX_STATUS_TIME_FORMAT "%I:%M %p"
   else
     tmux set-environment -g NORD_TMUX_STATUS_TIME_FORMAT "%H:%M"