Upgrade Ruby to 2.3.1
Upgrade Ruby to 2.3.1

This matches alphagov/govuk_frontend_toolkit@10aa7e00c7985bee3d59bf8c784be0176249d743
and is required to install activesupport 5.0.1.

alphagov/govuk_frontend_toolkit_gem,alphagov/govuk_frontend_toolkit_gem