Fix arm64 support darwin

[juan-pascale]

With this improvement, the tf versions without Darwin ARM64 support are replaced by the AMD64 version. This solves the following issue:

tfenv install 1.0.0

Installing Terraform v1.0.0
Downloading release tarball from https://releases.hashicorp.com/terraform/1.0.0/terraform_1.0.0_darwin_arm64.zip
curl: (22) The requested URL returned error: 404                                                                                                                                     

Tarball download failed

[rivernews]

Since this PR hasn't been merged, a note for anyone here for a solution to the 404 if you're using M1 machine (Apple Silicon), you can install 1.0.2 which is the first version Terraform supports ARM64.

[Zordrak]

This is good, but will be superseded by #351