Updated x11-server packages fix security vulnerabilities

In Xext/shm, the shmseg resource id can belong to a non-existing client and abort X server with FatalError “client not in use”, or overwrite existing segment of another existing client (CVE-2017-13721). Generating strings for XKB data used a single shared static buffer, which offered several opportunities for errors when strings end up longer than anticipated (CVE-2017-13723).