[tmux] Add second prefix

tmux/.tmux.conf

@@ -4,11 +4,8 @@ set -g default-terminal "xterm-256color"
 set -g history-limit 20000
 
 # Remap prefix
-unbind C-b
 set-option -g prefix C-a
-bind-key C-a send-prefix
-bind-key -n C-b send-keys C-b
-bind-key -n C-b send-prefix
+set-option -g prefix2 C-b
 
 setw -g mode-keys vi
 set-option -g status-keys vi