Stop signing releases (#77)

The key stopped producing correct signatures when upgrading MacOS,
at least when used by `twine`.

Author: Byron

Makefile

@@ -16,7 +16,7 @@ release:: clean
 force_release:: clean
 	git push --tags
 	python3 setup.py sdist bdist_wheel
-	twine upload -s -i 27C50E7F590947D7273A741E85194C08421980C9 dist/*
+	twine upload dist/*
 
 doc:: 
 	make -C doc/ html