Update Express from 3.4.0 to 3.4.7

https://github.com/visionmedia/express/compare/3.4.0...3.4.7

https://github.com/visionmedia/express/blob/3.4.7/History.md

This release includes lots of updates to Connect, the middleware Express
is based on. It also adds a res.vary() method to set the Vary header and
a load of other bugfixes.
Merge pull request #108 from alphagov/update-express-3-4-7

Update Express from 3.4.0 to 3.4.7