move docker-build outside of normal build target

This makes it much easier to rebuild the project by itself if you don't need updated deps or the full image

Author: Carson Anderson

auth_server/Makefile

@@ -26,9 +26,11 @@ build-local: update-deps
 ca-certificates.crt:
 	cp $(CA_BUNDLE) .
 
-build build-cross docker-build: update-deps godep ca-certificates.crt
+docker-build:
 	docker run --rm -v $(PWD):/src -e COMPRESS_BINARY=$(COMPRESS_BINARY) $(BUILDER_OPTS-$@) $(BUILDER_IMAGE)$(BUILDER_IMAGE_EXTRA-$@) $(IMAGE)
 
+build build-cross: update-deps godep ca-certificates.crt docker-build
+
 docker-tag-%:
 	docker tag -f $(IMAGE):latest $(IMAGE):$*