- adjust Makefile syntax

Makefile

@@ -1,19 +1,18 @@
-DOCKER_IMAGE_NAME=adnanh/webhook
-CONTAINER_NAME=webhook
+DOCKER_IMAGE_NAME = adnanh/webhook
+CONTAINER_NAME = webhook
 COMMIT := $(shell git rev-parse HEAD)
 SHORTCOMMIT := $(shell git rev-parse HEAD|cut -c-7)
 TEMPDIR := $(shell mktemp -d)
 
 
 docker-build: Dockerfile
-	docker build --force-rm=true --tag=${DOCKER_IMAGE_NAME} .
+	docker build --force-rm=true --tag=$(DOCKER_IMAGE_NAME) .
 
 docker-run:
 	@echo "Here's an example command on how to run a webhook container:"
-	@echo "docker run -d -p 9000:9000 -v /etc/webhook:/etc/webhook --name=${CONTAINER_NAME} \\"
-	@echo "  ${DOCKER_IMAGE_NAME} -verbose -hooks=/etc/webhook/hooks.json -hotreload"
+	@echo "docker run -d -p 9000:9000 -v /etc/webhook:/etc/webhook --name=$(CONTAINER_NAME) \\"
+	@echo "  $(DOCKER_IMAGE_NAME) -verbose -hooks=/etc/webhook/hooks.json -hotreload"
 
 build_rpm:
 	git archive --format=tar.gz --prefix webhook-$(COMMIT)/ --output $(TEMPDIR)/webhook-$(SHORTCOMMIT).tar.gz $(COMMIT)
 	rpmbuild -ta --define "_commit $(COMMIT)" $(TEMPDIR)/webhook-$(SHORTCOMMIT).tar.gz
-