Update Makefile to make more portable

Author: nicholasjackson

product-api/Makefile

@@ -1,7 +1,11 @@
 .DEFAULT_GOAL := swagger
 
-check_install:
-	which swagger || GO111MODULE=off go get -u github.com/go-swagger/go-swagger/cmd/swagger
+install_swagger:
+	go get -u github.com/go-swagger/go-swagger/cmd/swagger
 
-swagger: check_install
-	GO111MODULE=off swagger generate spec -o ./swagger.yaml --scan-models
+swagger:
+	@echo Ensure you have the swagger CLI or this command will fail.
+	@echo You can install the swagger CLI with: go get -u github.com/go-swagger/go-swagger/cmd/swagger
+	@echo ....
+
+	swagger generate spec -o ./swagger.yaml --scan-models