Update actix-gcd example to use actix-web 4.1.

actix-gcd/Cargo.toml

@@ -8,5 +8,5 @@ edition = "2018"
 # https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-actix-web = "1.0.8"
+actix-web = "4.1"
 serde = { version = "1.0", features = ["derive"] }

actix-gcd/src/main.rs

@@ -1,6 +1,7 @@
 use actix_web::{web, App, HttpResponse, HttpServer};
 
-fn main() {
+#[actix_web::main]
+async fn main() {
     let server = HttpServer::new(|| {
         App::new()
             .route("/", web::get().to(get_index))
@@ -10,10 +11,12 @@ fn main() {
     println!("Serving on http://localhost:3000...");
     server
         .bind("127.0.0.1:3000").expect("error binding server to address")
-        .run().expect("error running server");
+        .run()
+        .await
+        .expect("error running server");
 }
 
-fn get_index() -> HttpResponse {
+async fn get_index() -> HttpResponse {
     HttpResponse::Ok()
         .content_type("text/html")
         .body(
@@ -35,7 +38,7 @@ struct GcdParameters {
     m: u64,
 }
 
-fn post_gcd(form: web::Form<GcdParameters>) -> HttpResponse {
+async fn post_gcd(form: web::Form<GcdParameters>) -> HttpResponse {
     if form.n == 0 || form.m == 0 {
         return HttpResponse::BadRequest()
             .content_type("text/html")