add missing submission-id arg to download-old-submission

Author: Heliozoa

tmc-langs-cli/src/app.rs

@@ -424,6 +424,11 @@ pub fn create_app() -> App<'static, 'static> {
                     .long("exercise-id")
                     .required(true)
                     .takes_value(true))
+                .arg(Arg::with_name("submission-id")
+                    .help("The ID of the submission.")
+                    .long("submission-id")
+                    .required(true)
+                    .takes_value(true))
                 .arg(Arg::with_name("output-path")
                     .help("Path to where the submission should be downloaded.")
                     .long("output-path")