Upgrade Tor Browser Windows builds to cygwin 2.7.0
cygwin 2.7.0 contains a fix that re-enables Windows automatic TCP buffer tuning:
https://github.com/mirror/newlib-cygwin/commit/609d2b22afc63d80029a4fe85e64b51c84ccae08
This will benefit Windows users on high-bandwidth or high-latency links. It will also make a huge difference to Windows relay operators.