title: airline.vim does not work inside tmux
body: <p>I am new to tmux and also not an expert on VIM, I tried to use tmux these days, but seems that airline disappeared when I used vim inside tmux. I would like to show you the screen shots and hopefully anyone can help me solve this problem.</p>
  
  <p><a href="http://i.stack.imgur.com/Rf5rC.jpg" rel="noreferrer">airline in vim</a></p>
  
  <p><a href="http://i.stack.imgur.com/i9Qcs.jpg" rel="noreferrer">airline inside tmux</a></p>