change nested key for tmux to s

tmux.server.conf

@@ -5,9 +5,9 @@ setw -g aggressive-resize on
 
 # command prefix
 unbind C-b
-set -g prefix C-w
-bind w send-prefix
-bind-key C-w last-window
+set -g prefix C-s
+bind s send-prefix
+bind-key C-s last-window
 
 # basic settings
 set -g history-limit 30000