title: express.js compress middleware do not work
body: <p>I have the following middlewares in my app:</p>
  
  <pre><code>app.use(express.favicon(__dirname + '/static/public/images/favicon.ico'));
  app.use(express.compress());
  app.use(express.json());
  app.use(express.urlencoded());
  app.use(express.cookieParser('SECRET!'));
  app.use(express.static(__dirname + config.static_path, {maxAge: 365 * 86400000}));
  app.use(express.session({secret: 'SECRET!'}));
  app.use(flash());
  app.use(passport.initialize());
  app.use(passport.session());
  app.use(app.router);
  </code></pre>
  
  <p>headers example:
  <img src="https://i.stack.imgur.com/w5nWx.png" alt="jquery.js headers"></p>
  
  <p>But the static content do not compressing. What could be the problem?</p>