Although this command is removed in Terraform 0.13, our documentation is
for all versions of Terraform that remain in common use and keeping this
documented will be helpful for folks who are still using Terraform 0.11
and planning their upgrades to Terraform 0.12.
Both of the upgrade commands now include notes that they are only
available in their specific major version, along with a link to the
relevant upgrade guide for other background information about the upgrade,
in case the user finds the command documentation first. (The command docs
are, I think, a little more discoverable than the upgrade guides.)
Martin Atkins