Fix rust 2018 idioms warnings (#1092)

* Fix elided-lifetimes-in-paths warnings

Enabling `-Wrust-2018-idioms` generates `-Welided-lifetimes-in-paths`
warnings about hidden lifetime parameters in types being deprecated

* Unused extern crate

mixnode/src/node/http/mod.rs

@@ -5,6 +5,6 @@ pub(crate) mod verloc;
 use rocket::Request;
 
 #[catch(404)]
-pub(crate) fn not_found(req: &Request) -> String {
+pub(crate) fn not_found(req: &Request<'_>) -> String {
     format!("I couldn't find '{}'. Try something else?", req.uri())
 }