Fix the reboot script to use posix conditional.

tmux/tmux.conf

@@ -546,7 +546,7 @@ tmux_conf_theme_right_separator_sub='\uE0B3'  #   PowerlineSymbols.otf font, see
 #     - #{username}
 #     - #{username_ssh}
 tmux_conf_theme_status_left=" #{host_short}#[blink,fg=$tmux_conf_theme_colour_8]#{reboot}#[noblink,fg=$tmux_conf_theme_colour_6] | #S#{root} "
-tmux_conf_theme_status_right=" , #{?battery_status,#{battery_status}, Ok }#{?battery_bar,#{battery_bar},}#{?battery_percentage, #{battery_percentage},} | #{prefix}#{mouse}| %b %d | %R "
+tmux_conf_theme_status_right=" , #{?battery_status,#{battery_status}, OK }#{?battery_bar,#{battery_bar},}#{?battery_percentage, #{battery_percentage},} | #{prefix}#{mouse}| %b %d | %R "
 # uptime: up #{?uptime_y, #{uptime_y}y,}#{?uptime_d, #{uptime_d}d,}#{?uptime_h, #{uptime_h}h,}#{?uptime_m, #{uptime_m}m,}
 # status left style
 tmux_conf_theme_status_left_fg="$tmux_conf_theme_colour_6,$tmux_conf_theme_colour_7"
@@ -721,7 +721,7 @@ tmux_conf_update_plugins_on_reload=false
 # }
 #
 # reboot() {
-#   [[ -f /var/run/reboot-required ]] && echo ' [REBOOT]'
+#   [ -f /var/run/reboot-required ] && echo ' [REBOOT]'
 # }
 #
 # "$@"