Log Message:
py-virtualenv: updated to 16.3.0

v16.3.0:

Bugfixes

Use importlib over deprecated imp in distutils/__init__.py for python 3
Preserve cert option defined in pip.conf or environment variable.
fixed a ResourceWarning: unclosed file in call_subprocess()
pre-import some built-in modules in site.py on PyPy according to PyPy’s site.py
Copy files from sys.exec_prefix only if it is really different path than used prefix