(PUP-3479) Update Windows ffi dependency to new ffi

Ruby 2.1.3 on Windows requires ffi 1.9.5. Update our Windows dependencies
to allow 1.9.5+ to be selected.
Merge pull request #3202 from MikaelSmith/maint/master/update-ffi-ruby-213

(PUP-3479) Update Windows ffi dependency to new ffi