message: try to fix travis build (6)
diff: @@ -4,7 +4,14 @@ use opencv::highgui;
  #[test]
  fn callback() {
  - if let Ok(..) = highgui::named_window("test", 0) {
  + #[cfg(target_os = "linux")]
  + {
  + // only run under X11 if on linux
  + if std::env::var("DISPLAY").is_err() {
  + return;
  + }
  + }
  + highgui::named_window("test", 0).unwrap();
  let mut value = 50;
  let cb_value = Arc::new(Mutex::new(0));
  highgui::create_trackbar("test_track", "test", &mut value, 100, Some(Box::new({
  @@ -17,5 +24,4 @@ fn callback() {
  assert_eq!(value, 10);
  assert_eq!(*cb_value.lock().unwrap(), 10);
  }
  -}
  