[#4559] update installation.rst to match README's virtualenv name
[#4559] update installation.rst to match README's virtualenv name

heiths/allura,apache/incubator-allura,apache/incubator-allura,lym/allura-git,lym/allura-git,heiths/allura,lym/allura-git,apache/allura,apache/allura,apache/incubator-allura,heiths/allura,apache/allura,lym/allura-git,apache/allura,apache/allura,heiths/allura,heiths/allura,lym/allura-git,apache/incubator-allura