Fix HashMap in rustdoc example

Author: jurvis

lightning-invoice/src/payment.rs

@@ -34,7 +34,10 @@
 //! #
 //! # #[cfg(feature = "no-std")]
 //! # extern crate core2;
+//! # #[cfg(feature = "no-std")]
+//! # extern crate hashbrown;
 //! #
+//! # use hashbrown::HashMap;
 //! # use lightning::ln::{PaymentHash, PaymentPreimage, PaymentSecret};
 //! # use lightning::ln::channelmanager::{ChannelDetails, PaymentId, PaymentSendFailure};
 //! # use lightning::ln::msgs::LightningError;
@@ -80,7 +83,7 @@
 //! # impl Router for FakeRouter {
 //! # 	fn find_route(
 //! # 		&self, payer: &PublicKey, params: &RouteParameters, payment_hash: &PaymentHash,
-//! # 		first_hops: Option<&[&ChannelDetails]>, inflight_htlc_map: std::collections::HashMap<(u64, bool), u64>
+//! # 		first_hops: Option<&[&ChannelDetails]>, inflight_htlc_map: HashMap<(u64, bool), u64>
 //! # 	) -> Result<Route, LightningError> { unimplemented!() }
 //! #
 //! #   fn payment_path_failed(&self, path: Vec<&RouteHop>, short_channel_id: u64) {  unimplemented!() }