Fix actix-http examples (#1259)

Fix actix-http examples

actix-http/examples/echo.rs

@@ -7,7 +7,8 @@ use futures::StreamExt;
 use http::header::HeaderValue;
 use log::info;
 
-fn main() -> io::Result<()> {
+#[actix_rt::main]
+async fn main() -> io::Result<()> {
     env::set_var("RUST_LOG", "echo=info");
     env_logger::init();
 
@@ -37,4 +38,5 @@ fn main() -> io::Result<()> {
                 .tcp()
         })?
         .run()
+        .await
 }