Open problem pages in the reverse order

[estshorter]

Currently, cargo compete open open pages in ascending order of difficulty (A to F in AtCoder), but I think this should be done in the reverse order.
This is because the most difficult problem is shown in a browser after executing the command.

possibly related code:

cargo-compete/src/open.rs

Lines 17 to 21 in 8a148d9

	for url in urls {
	let url = url.borrow();
	shell.status("Opening", url)?;
	opener::open(url.as_str())?;
	}