elan-cli messed up with progess

[acasta-yhliu]

src/elan-cli/download_tracker.rs messed up the download progress. There are messages all over the screen. I see that it says:

// delete_line() doesn't seem to clear the line properly.
// Instead, let's just print some whitespace to clear it.
let _ = write!(self.term.as_mut().unwrap(), "                ");

maybe print \r would be a better choice in case delete_line() does not work.