Error with `make release_diff`

Here are the code snippets in Makefile related to the release_diff command:

.PHONY: release_diff
release_diff: $(REPORTDIR)/release-diff.md

ONTBASE=          https://w3id.org/cpont/ontology
CURRENT_RELEASE=  $(ONTBASE).owl

$(TMPDIR)/current-release.owl:
	wget $(CURRENT_RELEASE) -O $@

$(REPORTDIR)/release-diff.md: $(ONT).owl $(TMPDIR)/current-release.owl
	$(ROBOT) diff --labels true --left $(TMPDIR)/current-release.owl --right $(ONT).owl -f markdown -o $@

The wget command fails since https://w3id.org/cpont/ontology.owl doesn't exist.

ONTBASE is constructed from the uribase and uribase_suffix values defined in cpont-odk.yaml.