* fix: broken link

Fixed the pdf link of broken C++ Cheat Sheet.
Issue No. #5378

* Update more/free-programming-cheatsheets.md
Co-authored-by: NDavid Ordás <davorpatech@gmail.com>
Co-authored-by: NEric Hellman <eric@hellman.net>
Co-authored-by: NDavid Ordás <davorpatech@gmail.com>