Upgrade dev VM to Puppet 3.6
Upgrade dev VM to Puppet 3.6

Upgrade the Vagrant box versions in `development/Vagrantfile` to use the
latest box images which install Puppet 3.6 by default.

Without this, Puppet will upgrade itself to version 3.6 but will show
errors on the first run.

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