release version 6

[dhellmann]

We need to skip 5 because we had the broken package with that version some time back.

[dhellmann]

Alpha version published https://github.com/python-virtualenvwrapper/virtualenvwrapper/releases/tag/6.0.0.0a1

[dhellmann]

Second alpha published https://github.com/python-virtualenvwrapper/virtualenvwrapper/releases/tag/6.0.0.0a2

[dhellmann]

@jasonamyers we've had the alpha out for 2 months, what do you think about making it official?

[carltongibson]

I think this can be closed now 😉