Made app::Task a winit-only feature

Not exactly sure why, but the wayland feature disables cosmic::app so this is required

src/lib.rs

@@ -22,7 +22,9 @@ pub use app::{Application, ApplicationExt};
 #[cfg(feature = "applet")]
 pub mod applet;
 
+#[cfg(feature = "winit")]
 pub use app::Task;
+
 pub mod task;
 
 pub mod config;