Remove HttpResponse, which is an unused import.
@@ -70,7 +70,7 @@ The full source of src/main.rs is listed below:
```rust
# use std::thread;
extern crate actix_web;
-use actix_web::{server, App, HttpRequest, HttpResponse};
+use actix_web::{server, App, HttpRequest};
fn index(req: HttpRequest) -> &'static str {
"Hello world!"
