Update govuk-frontend from 2.6.0 to 2.7.0
Update govuk-frontend from 2.6.0 to 2.7.0

This is so we can pick up govuk-prototype-kit.config.json file which
was added to govuk-frontend to support this extensions feature.

alphagov/govuk_prototype_kit,dwpdigitaltech/hrt-prototype,alphagov/govuk_prototype_kit,dwpdigitaltech/hrt-prototype,alphagov/govuk_prototype_kit,dwpdigitaltech/hrt-prototype