updated make file

Makefile

@@ -25,6 +25,7 @@ clean-pyc:
 	find . -name '*.pyo' -exec rm -f {} +
 	find . -name '*~' -exec rm -f {} +
 	find . -name '__pycache__' -exec rm -fr {} +
+	find . -name '.pytest_cache' -exec rm -fr {} +
 
 install: clean
 	python setup.py install