Minor update to makefile, update virtualenv, pip

Makefile

@@ -1,6 +1,6 @@
-.PHONY: clean_env init_env clean_virtualenv install_packages clean install run all schema_seminar.pdf schema_all.pdf
+.PHONY: clean_env init_env clean_virtualenv install_packages clean install run all schema_seminar.pdf schema_all.pdf virtualenv
 PYTHON=python2.7
-VE_VER=12.0.7
+VE_VER=13.1.2
 LOCAL_PYTHON=bin/python
 
 all: install
@@ -17,7 +17,7 @@ make_env: ${LOCAL_PYTHON}
 
 # phony, but fast repeated execution
 install_packages: make_env
-	bin/pip install -r requirements.txt
+	bin/pip install -r requirements.txt --upgrade
 
 # phony
 clean_env:
@@ -41,6 +41,7 @@ virtualenv:
 # phony
 clean_virtualenv:
 	rm -rf virtualenv/
+	rm -rf virtualenv-*.tar.gz
 
 run:
 	./manage.py runserver_plus