Deprecated tox -downloadcache option removed
Deprecated tox -downloadcache option removed

Caching is enabled by default from pip version 6.0

More info:
https://testrun.org/tox/latest/config.html#confval-downloadcache=path
https://pip.pypa.io/en/stable/reference/pip_install/#caching

Change-Id: Ib6e42f616ecf79d5f701a08e433d5c0f638369dd

openstack/xstatic-angular-gettext,stackforge/xstatic-angular-gettext