Fix compilation in payment rustdoc examples

The samples were not valid rust, but previous versions of rustc had
a bug where they were accepted anyway. Latest rustc beta no longer
accepts these.

Author: TheBlueMatt

lightning-invoice/src/payment.rs

@@ -63,15 +63,15 @@
 //! #     ) -> Result<(), PaymentSendFailure> { unimplemented!() }
 //! # }
 //! #
-//! # struct FakeRouter {};
+//! # struct FakeRouter {}
 //! # impl<S: Score> Router<S> for FakeRouter {
 //! #     fn find_route(
 //! #         &self, payer: &PublicKey, params: &RouteParameters, payment_hash: &PaymentHash,
 //! #         first_hops: Option<&[&ChannelDetails]>, scorer: &S
 //! #     ) -> Result<Route, LightningError> { unimplemented!() }
 //! # }
 //! #
-//! # struct FakeScorer {};
+//! # struct FakeScorer {}
 //! # impl Writeable for FakeScorer {
 //! #     fn write<W: Writer>(&self, w: &mut W) -> Result<(), std::io::Error> { unimplemented!(); }
 //! # }
@@ -82,7 +82,7 @@
 //! #     fn payment_path_failed(&mut self, _path: &[&RouteHop], _short_channel_id: u64) {}
 //! # }
 //! #
-//! # struct FakeLogger {};
+//! # struct FakeLogger {}
 //! # impl Logger for FakeLogger {
 //! #     fn log(&self, record: &Record) { unimplemented!() }
 //! # }