Fix copy modes for tmux 2.4 and later

tmux/tmux#754 describes the change of
configuration syntax, this fixes yank to system clipboard from copy
mode.

.tmux.conf

@@ -65,10 +65,10 @@ setw -g window-status-current-fg blue
 set -g pane-active-border-fg blue
 
 # move tmux copy buffer into x clipboard
-bind-key -t vi-copy y copy-pipe 'xclip -d :0 -selection clipboard >/dev/null'
+bind-key -T copy-mode-vi y send-keys -X copy-pipe 'xclip -d :0 -selection clipboard >/dev/null'
 
 # allow tmux rectangular select
-bind-key -t vi-copy r rectangle-toggle
+bind-key -T copy-mode-vi r send-keys -X rectangle-toggle
 
 # Bind new window to create default layout
 bind c new-window\; splitw\; splitw\; select-layout d1aa,202x72,0,0{124x72,0,0,0,77x72,125,0[77x36,125,0,1,77x35,125,37,2]}\; select-pane -t 1