fix a mistake in the Box<dyn HttpClient> implementation

Author: jbr

src/lib.rs

@@ -70,6 +70,6 @@ pub type Error = http_types::Error;
 #[async_trait]
 impl HttpClient for Box<dyn HttpClient> {
     async fn send(&self, req: Request) -> Result<Response, Error> {
-        self.send(req).await
+        self.as_ref().send(req).await
     }
 }