Add missing pip requirement to virtualenv

utils/Makefile

@@ -45,7 +45,7 @@ virtualenv:
 	virtualenv $(NAME)env
 	. $(NAME)env/bin/activate && pip install -r requirements.txt
 	. $(NAME)env/bin/activate && pip install setuptools --upgrade
-	. $(NAME)env/bin/activate && pip install enum configparser pylint pep8 nose coverage mock flake8 PyYAML click
+	. $(NAME)env/bin/activate && pip install enum configparser pylint pep8 nose coverage mock flake8 PyYAML click backports.functools_lru_cache
 
 #       If there are any special things to install do it here
 #       . $(NAME)env/bin/activate && INSTALL STUFF