Fix deprecation warning in routes.

We were getting the following message:

DEPRECATION WARNING: redirect blocks with arity of 1 are deprecated.
Your block must take 2 parameters: the environment, and a request
object. (called from block in <top (required)> at
/var/govuk/publisher/config/routes.rb:28)
Merge pull request #158 from alphagov/fix_deprecation_warning

Fix deprecation warning in routes.