Fix `make -f docker.Makefile cross` doing more than it should
Before this fix, the target being empty, it would build the whole
`Dockerfile` instead of just the `cross` target.
@@ -27,7 +27,7 @@ shell: build_dev_image ## run a shell in the docker build image
docker run -ti --rm $(DEV_IMAGE_NAME) bash
cross: create_bin ## cross-compile binaries (linux, darwin, windows)
- docker build --target=$* -t $(CROSS_IMAGE_NAME) .
+ docker build --target=cross -t $(CROSS_IMAGE_NAME) .
docker create --name $(CROSS_CTNR_NAME) $(CROSS_IMAGE_NAME) noop
docker cp $(CROSS_CTNR_NAME):$(PKG_PATH)/bin/$(BIN_NAME)-linux bin/$(BIN_NAME)-linux
docker cp $(CROSS_CTNR_NAME):$(PKG_PATH)/bin/$(BIN_NAME)-darwin bin/$(BIN_NAME)-darwin
