title: "set-window-option -g mode-keys vi" doesn't work in .tmux.conf
body: <p>I've been able to turn-on the vi-mode inside tmux successfully by pressing <code>C-a :</code> (I've changed default prefix) and then typing <code>set-window-option mode-keys vi</code>. However, I can't make it stick by adding into <code>~/.tmux.conf</code>. Here is my config:</p>
  
  <pre><code># Change default prefix key to C-a
  unbind-key C-b
  set -g prefix 'C-a'
  bind-key 'C-a' send-prefix
  
  # Configure Vim mode for navigating text and selection
  set-window-option -g mode-keys vi
  bind-key -t vi-copy 'v' begin-selection
  bind-key -t vi-copy 'y' copy-selection
  
  # Allow navigating panes with vi-like commands.
  bind k selectp -U
  bind j selectp -D
  bind h selectp -L
  bind l selectp -R
  </code></pre>
  
  <p>Notably, navigating panes using <code>kjhl</code> keys also doesn't work. Perhaps this is because tmux fails to execute set-window-option earlier in the script. What's wrong here?</p>