Fix backend_session_udev without backend_udev
@@ -23,7 +23,7 @@ extern crate drm;
extern crate gbm;
#[cfg(feature = "backend_libinput")]
extern crate input;
-#[cfg(feature = "backend_udev")]
+#[cfg(feature = "udev")]
extern crate udev;
/*
#[cfg(feature = "backend_session_logind")]
