[tmux]: renumber windows to always keep a gapless order.

.tmux.conf

@@ -3,6 +3,8 @@ set-option -g default-terminal "screen-256color"
 
 # Enumerate windows from 1
 set -g base-index 1
+# Renumber windows when one is closed to keep a gapless order
+set-option -g renumber-windows on
 
 # Lower escape-time in vim
 # see https://github.com/neovim/neovim/wiki/FAQ#esc-in-tmux-or-gnu-screen-is-delayed