Prior to this commit, the docker action was using the method `prefix` on an IPv4 and IPv6 address. This works fine for ruby versions 2.5 and newer, however the ruby shipped with Vagrant is before 2.5, and therefore the IPv4 and IPv6 classes do not have the prefix method, resulting in an error. This commit fixes that by using a different method of determining the prefix.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.