Install a specific version of terraform-docs

Note that this change is dependent on the merging of
cisagov/setup-env-github-action#31.

Co-authored-by: Nick M. <50747025+mcdonnnj@users.noreply.github.com>

.github/workflows/build.yml

@@ -85,7 +85,9 @@ jobs:
           sudo mv /usr/local/bin/terraform /usr/local/bin/terraform-default
           sudo ln -s /opt/terraform/terraform /usr/local/bin/terraform
       - name: Install Terraform-docs
-        run: GO111MODULE=on go get github.com/terraform-docs/terraform-docs
+        run: |
+          GO111MODULE=on go get \
+            github.com/terraform-docs/terraform-docs@${TERRAFORM_DOCS_VERSION}
       - name: Find and initialize Terraform directories
         run: |
           for path in $(find . -not \( -type d -name ".terraform" -prune \) \