[#52201683] Updated puppet's config.ru from upstream
[#52201683] Updated puppet's config.ru from upstream

Details in comments in the file. Puppet commits that correspond to the
change:
* https://github.com/puppetlabs/puppet/commit/38cba0a4294aba696f6184f3c5b91c2a569c7fed#ext/rack/files/config.ru
* https://github.com/puppetlabs/puppet/commit/623fa028147a3eb6602c8911a437d210ce56990b#ext/rack/files/config.ru
* https://github.com/puppetlabs/puppet/commit/0cea47ec90e77e81c27ffbedbd46bb5357a45d66#ext/rack/files/config.ru

This config.ru is backwards compatible (tested on vagrant setup)

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