test(files): Fix doctest import

src/files/mod.rs

@@ -38,13 +38,14 @@ type HttpNewService = BoxServiceFactory<(), ServiceRequest, ServiceResponse, Act
 /// ```rust
 /// use std::{
 ///   convert::TryInto,
-///   sync::{Arc, RwLock},
+///   sync::Arc,
 /// };
 /// use actix_web::App;
 /// use espresso::{
 ///   files::Files,
 ///   config::ServerConfig,
 /// };
+/// use tokio::sync::RwLock;
 ///
 /// let mut server_config = ServerConfig::default();
 ///