Prefer the newer "go install" syntax

As of [Go 1.16](https://tip.golang.org/doc/go1.16#go-command) the `GO111MODULE` environment variable defaults to `on` and `go get` has been deprecated for module installation.

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

.github/workflows/build.yml

@@ -88,7 +88,7 @@ jobs:
           sudo ln -s /opt/terraform/terraform /usr/local/bin/terraform
       - name: Install Terraform-docs
         run: |
-          GO111MODULE=on go get \
+          go install \
             github.com/terraform-docs/terraform-docs@${TERRAFORM_DOCS_VERSION}
       - name: Find and initialize Terraform directories
         run: |