Bump govuk_template_jinja to 0.19.0
Bump govuk_template_jinja to 0.19.0

https://github.com/alphagov/govuk_template/blob/master/CHANGELOG.md

- Remove external link styles (PR #231)
- Remove extraneous copy of HTML5shiv that wasn’t being used (PR #254)
- Update govuk_frontend_toolkit to latest version (PR #256)

alphagov/govuk_elements,alphagov/govuk_elements,alphagov/govuk_elements,alphagov/govuk_elements