Terraform and terraform-validator versions are out-of-date

[renato-rudnicki]

Terraform and terraform-validator are out-of-date on user guide. Currently, user guide is mentioning gs://terraform-validator/releases/2019-04-04/terraform-validator-windows-amd64 and Terraform v0.11 which aren't the latest one.

See https://github.com/forseti-security/policy-library/blob/master/docs/user_guide.md#install-terraform-validator