Add missing make build target

Author: rasmunk

Makefile

@@ -19,6 +19,9 @@ rootfs:
 	@cp config.json ./plugin/
 	@docker rm -vf tmp
 
+build:
+	@docker build -q -t ${PLUGIN_NAME}:${PLUGIN_TAG} .
+
 create:
 	@echo "### remove existing plugin ${PLUGIN_NAME}:${PLUGIN_TAG} if exists"
 	@docker plugin rm -f ${PLUGIN_NAME}:${PLUGIN_TAG} || true