Make Ubuntu callout correct (#10883)

Author: ericholscher

docs/user/config-file/v2.rst

@@ -354,7 +354,7 @@ build.apt_packages
 ``````````````````
 
 List of `APT packages`_ to install.
-Our build servers run Ubuntu 18.04, with the default set of package repositories installed.
+Our build servers run various Ubuntu LTS versions with the default set of package repositories installed.
 We don't currently support PPA's or other custom repositories.
 
 .. _APT packages: https://packages.ubuntu.com/