pam_u2f: update meta

pkgs/os-specific/linux/pam_u2f/default.nix

···
   meta = with lib; {
     homepage = "https://developers.yubico.com/pam-u2f/";
     description = "A PAM module for allowing authentication with a U2F device";
+    changelog = "https://github.com/Yubico/pam-u2f/raw/pam_u2f-${version}/NEWS";
     license = licenses.bsd2;
     platforms = platforms.unix;
     maintainers = with maintainers; [ philandstuff ];