update packaging URLs

fix a broken URL for fedora RPM packaging guide and fix a URL redirect for Slackware packaging guide.

Author: partev

Doc/using/unix.rst

@@ -30,9 +30,9 @@ following links:
       for Debian users
    https://en.opensuse.org/Portal:Packaging
       for OpenSuse users
-   https://docs-old.fedoraproject.org/en-US/Fedora_Draft_Documentation/0.1/html/RPM_Guide/ch-creating-rpms.html
+   https://docs.fedoraproject.org/en-US/package-maintainers/Packaging_Tutorial_GNU_Hello/
       for Fedora users
-   http://www.slackbook.org/html/package-management-making-packages.html
+   https://slackbook.org/html/package-management-making-packages.html
       for Slackware users