[Twisted-Python] buildbots: normal service will resume shortly

[Glyph]

> On Jun 3, 2016, at 00:39, Glyph <glyph at twistedmatrix.com> wrote:
> 
> We had a minor hiccup earlier today due partially to a new Cryptography release (the Windows builders, which started spuriously failing builds) and some random networking issues (the OS X builders, which went offline).  I believe I've gotten them back online and performing to spec and they should chew through their respective backlogs shortly.

Oops!  The _actual_ bug on Windows appears to be a regression in virtualenv, which I have filed here - https://github.com/pypa/virtualenv/issues/929 - which I've now downgraded to 15.0.1 to work around it for now.

-glyph