chore(lib): fix unused_mut warnings from newest nightly

src/proto/h2/client.rs

@@ -97,7 +97,7 @@ where
                 State::Ready(ref mut tx, ref conn_dropper) => {
                     try_ready!(tx.poll_ready().map_err(::Error::new_h2));
                     match self.rx.poll() {
-                        Ok(Async::Ready(Some((req, mut cb)))) => {
+                        Ok(Async::Ready(Some((req, cb)))) => {
                             // check that future hasn't been canceled already
                             if cb.is_canceled() {
                                 trace!("request canceled");

tests/client.rs

@@ -214,7 +214,7 @@ macro_rules! test {
     ) => ({
         let server = TcpListener::bind("127.0.0.1:0").expect("bind");
         let addr = server.local_addr().expect("local_addr");
-        let mut rt = $runtime;
+        let rt = $runtime;
 
         let connector = ::hyper::client::HttpConnector::new(1);
         let client = Client::builder()
@@ -222,7 +222,7 @@ macro_rules! test {
             .http1_title_case_headers($title_case_headers)
             .build(connector);
 
-        #[allow(unused_assignments)]
+        #[allow(unused_assignments, unused_mut)]
         let mut body = Body::empty();
         let mut req_builder = Request::builder();
         $(