Update async-std tests

tests/transport_file.rs

@@ -35,10 +35,11 @@ mod test {
         remove_file(file).unwrap();
     }
 
-    #[cfg(feature = "async")]
+    #[cfg(feature = "async-std1")]
     #[async_attributes::test]
     async fn file_transport_async() {
-        use lettre::r#async::Transport;
+        use lettre::AsyncStd1Transport;
+
         let sender = FileTransport::new(temp_dir());
         let email = Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())

tests/transport_sendmail.rs

@@ -20,10 +20,11 @@ mod test {
         assert!(result.is_ok());
     }
 
-    #[cfg(feature = "async")]
+    #[cfg(feature = "async-std1")]
     #[async_attributes::test]
     async fn sendmail_transport_async() {
-        use lettre::r#async::Transport;
+        use lettre::AsyncStd1Transport;
+
         let sender = SendmailTransport::new();
         let email = Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())

tests/transport_stub.rs

@@ -17,10 +17,11 @@ fn stub_transport() {
     sender_ko.send(&email).unwrap_err();
 }
 
-#[cfg(feature = "async")]
+#[cfg(feature = "async-std1")]
 #[async_attributes::test]
 async fn stub_transport_async() {
-    use lettre::r#async::Transport;
+    use lettre::AsyncStd1Transport;
+
     let sender_ok = StubTransport::new_ok();
     let sender_ko = StubTransport::new_error();
     let email = Message::builder()