Use SSLV3 for HMRC update server access

Not sure if this happened just today on HMRC end or my OSX Mavericks update
is to blame, but I cannot access update server any longer with I leave
SSL version unset. This change sorts it out.
Merge pull request #111 from alphagov/force-sslv3-when-downloading-updates

Use SSLV3 for HMRC update server access