fixing doc test

Author: Sharmalm

lightning/src/onion_message/messenger.rs

@@ -70,7 +70,9 @@ use crate::prelude::*;
 /// # use std::sync::Arc;
 /// # struct FakeLogger;
 /// # impl Logger for FakeLogger {
-/// #     fn log(&self, record: &Record) { unimplemented!() }
+/// #     fn log(&self, record: &Record) {
+/// #     println!("{:?}" , record); 
+/// #     }
 /// # }
 /// # struct FakeMessageRouter {}
 /// # impl MessageRouter for FakeMessageRouter {