update link for OpenVZ (#3241)

previous docs were from 2005, found more recent docs from 2018

free-programming-books.md

@@ -1736,7 +1736,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Linux Newbie Administrator Guide](http://lnag.sourceforge.net)
 * [Linux Security for Beginners](http://www.linuxtopia.org/LinuxSecurity/index.html)
 * [Linux Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/linux) (PDF, Kindle) (email address *requested*, not required)
-* [OpenVZ Linux virtualization](http://download.openvz.org/doc/OpenVZ-Users-Guide.pdf) (PDF)
+* [OpenVZ Linux virtualization](https://docs.virtuozzo.com/pdf/virtuozzo_infrastructure_platform_quick_start_guide.pdf) (PDF)
 * [Red Hat Enterprise Linux 6 Essentials](http://www.techotopia.com/index.php/Red_Hat_Enterprise_Linux_6_Essentials)
 * [Secure Programming HOWTO - Creating Secure Software](http://www.dwheeler.com/secure-programs/) - D. A. Wheeler (HTML, PDF)
 * [Ten Steps to Linux Survival: Bash for Windows People](http://dullroar.com/book/TenStepsToLinuxSurvival.html) - Jim Lehmer