Fix Dockerfile compatibility with Alpine Linux

In order to support Alpine Linux the CGO_ENABLED=0 flag
is needed, which is set in .goreleaser.yml but was not
set in the Dockerfile.

Before this change the binary built via the Dockerfile
was not compatible with hashicorp/terraform base image,
which is based on Alpine Linux.

Author: Jordan Jennings

Dockerfile

@@ -3,7 +3,7 @@ WORKDIR /go/src/github.com/databrickslabs/databricks-terraform/
 RUN curl -sSL "https://github.com/gotestyourself/gotestsum/releases/download/v0.4.2/gotestsum_0.4.2_linux_amd64.tar.gz" | tar -xz -C /usr/local/bin gotestsum
 RUN curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.25.0
 COPY . .
-RUN make vendor build
+RUN CGO_ENABLED=0 make vendor build
 
 FROM hashicorp/terraform:latest
 COPY --from=0 /go/src/github.com/databrickslabs/databricks-terraform/terraform-provider-databricks /root/.terraform.d/plugins/