Restore caching behaviour of frontend no-cache assets.
Restore caching behaviour of frontend no-cache assets.

This was inadvertently removed with the decoupling of asset serving from
the static application.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet