Change to stable Rust 1.52

Fix clippy warnings that are new in this version.

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
-channel = "nightly-2021-01-31"
+channel = "1.52"
 components = ["clippy"]
 targets = ["armv7-unknown-linux-gnueabihf"]

swap/src/bin/asb.rs

@@ -353,7 +353,7 @@ async fn register_tor_services(
                 }
             })
         })
-        .filter_map(|details| details)
+        .flatten()
         .collect::<Vec<_>>();
 
     let key = seed.derive_torv3_key();

swap/src/protocol/alice/state.rs

@@ -308,8 +308,8 @@ impl State2 {
 
         let tx_cancel_sig = self.a.sign(tx_cancel.digest());
         Message3 {
-            tx_refund_encsig,
             tx_cancel_sig,
+            tx_refund_encsig,
         }
     }