Fix foreman run script to work with rbenv
Fix foreman run script to work with rbenv

Because foreman is starting one ruby process from another ruby process,
the second one was inheriting the parents rbenv setup, and therefore
ignoring the application's .ruby-version file.  Unsetting this env
variable fixes that.

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