make build-edge recently broke

Seems like ALPINE_IMG isn't being replaced, when running make build-edge, as such the build breaks

rasmus@alpine ~/P/docker-abuild> make build-edge
sed 's!%%ALPINE_TAG%%!edge!;s!%%ALPINE_REL%%!edge!' \
	Dockerfile.in >| Dockerfile
DOCKER_BUILDKIT=0 docker build $DOCKER_FLAGS \
  -t alpinelinux/docker-abuild:edge-x86_64 .
Sending build context to Docker daemon  184.3kB
Step 1/10 : FROM %%ALPINE_IMG%%/alpine:edge
invalid reference format: repository name must be lowercase
make: *** [Makefile:44: build-edge] Error 1