use builtin venv, and python3, also fail fast on tests..

Makefile

@@ -1,8 +1,8 @@
 MODULES=pasn1.py
-VIRTUALENV?=virtualenv-3.7
+VIRTUALENV?=python3 -m venv
 
 test:
-	(echo $(MODULES) | entr sh -c 'python -m coverage run -m unittest $(basename $(MODULES)) && coverage report --omit=p/\* -m -i')
+	(echo $(MODULES) | entr sh -c 'python -m coverage run -m unittest --failfast $(basename $(MODULES)) && coverage report --omit=p/\* -m -i')
 
 env:
 	($(VIRTUALENV) p && . ./p/bin/activate && pip install -r requirements.txt)